It was a burglary gone awry. That’s how it looked, at least, to the Los Angeles police detectives who arrived at a gated condo complex in the Van Nuys section of Los Angeles on the evening of February 24, 1986.

The body of a 29-year-old nurse and three-month newlywed, Sherri Rasmussen, had been discovered by her husband, John Ruetten. When Ruetten, an engineer, had come home from work at 5:55 p.m., he’d known instantly that something was wrong. The garage door was open and the silver two-door BMW he’d bought Rasmussen as an engagement gift was gone. It seemed strange that she would not be home; he knew she had called in sick to work that morning.

When Ruetten rushed inside, he found his wife’s body in the ransacked living room. Shards from a broken porcelain vase littered the floor. A TV wall unit was partially collapsed. A credenza drawer had been yanked out and its contents, mostly documents, dumped on the floor.

Examining the scene, the lead homicide detective, Lyle Mayer, began to piece together what he thought had taken place. Burglars must have entered through the unlocked front door. While one removed electronics from the wall unit, the other went upstairs and was surprised by Rasmussen. Her attire—robe, T-shirt, and panties—suggested she had not been expecting visitors.

Rasmussen was six feet tall and fit, and the ensuing struggle was ferocious. It evidently began in the dining room on the second floor of the townhouse, where shots were fired from a .38-caliber pistol, one of which may have hit Rasmussen. Hearing the shots, the downstairs burglar probably fled, ditching the video components. A blood trail down the stairs and a bloody handprint near the front door suggested Rasmussen had tried to escape or reach the panic button on the alarm panel located there, but her assailant followed. In the living room Rasmussen had been bitten on her left forearm, perhaps while grappling for the gun, and then struck over the head with the heavy vase, a blow that likely incapacitated her. The assailant had then taken a quilt from across the room—presumably to muffle the gun’s report—and fired more shots through it, killing Rasmussen. A housekeeper in the unit next door later said she’d heard a scuffle and a scream, but no gunshots. Imagining the din to be a domestic altercation, she hadn’t called the police.

In all, Rasmussen had been shot three times in the chest, the bullets piercing her heart, lungs, and spine. When it was over, the killer stole the BMW parked in the garage. That most items in the house appeared undisturbed—including Rasmussen’s jewelry box, sitting in plain view on her dresser—seemed to Mayer further evidence of a rushed exit.

It wasn’t until nearly two o’clock in the morning that Lloyd Mahany, a criminalist from the Los Angeles County coroner’s office, arrived to examine the body. It was his second homicide of the night. Mahany began by checking for trace evidence around the victim’s body—hair, fibers, anything unusual—but he found nothing of note. Next he opened a sexual-assault kit and collected a series of swabs and slides.

Sherri Rasmussen
Image courtesy of the Rasmussen family

When he noticed the bite mark on Rasmussen’s arm, Mahany selected a six-inch swab housed in a tube with a red rubber stopper. He removed the stopper and carefully swabbed the impression left by the assailant’s teeth. He reinserted the swab into the tube, squeezed the stopper shut, and labeled it with his initials and the coroner’s case number. He placed the tube inside a 5-by-7-inch L.A. coroner’s physical-evidence envelope, on which he wrote Sherri Rasmussen’s name, a description of the contents, and where he’d obtained them. Then he sealed it, noting the date and time he had done so.

The sun was just coming up over the San Fernando Valley when Mahany completed his work at the crime scene. He drove directly to the coroner’s office, where an evidence custodian booked the swab of the bite mark on Sherri Rasmussen’s arm into evidence at 10:32 a.m. on February 25, 1986.

Transcript of police interview with Stephanie Lazarus, June 5, 2009

Detective Jaramillo: I didn’t want to talk about this in the squad room, ’cause—

Stephanie Lazarus: Oh, that’s okay.

Detective Jaramillo: —I don’t know what people are listening … We’ve been assigned a case that we’ve been looking at … And reviewing the case, there’s some notes to see as far as your name being mentioned.

Stephanie Lazarus: Oh, okay.

Detective Jaramillo: Do you know John Ruetten?

Video: Watch key moments from Lazarus's interrogation

Nels and Loretta Rasmussen, Sherri’s parents, arrived in Los Angeles from Arizona the day after the murder. Nels immediately sought out Mayer, the homicide detective, who informed him that the police were looking for one or more burglars in connection with the killing. He also told Nels they had ruled out John Ruetten as a suspect. Nels mentioned that his daughter had complained one or two months earlier about an ex-girlfriend of her husband’s who had shown up at Sherri’s hospital one day and confronted her. Nels didn’t know the ex-girlfriend’s name, but he knew she was a Los Angeles police officer. In Nels’s mind, she was a prime suspect. Mayer made a note of the ex-girlfriend in the case file but apparently never followed up. The stolen BMW was found abandoned nearby about a week later, but it offered up no further clues.

Two months after the murder, a pair of men attempted a burglary a few blocks from Sherri’s condo. When Mayer learned that one of them had brandished a gun, these unidentified burglars became the focus of his homicide investigation. But the suspects remained elusive, and months passed without further leads. In late October, the Los Angeles Times ran a story on the now eight-month-old case, reporting that the Rasmussens were offering a $10,000 reward for any information regarding the suspects in their daughter’s murder, whom Mayer described in the article as two Latino men between 5 feet 4 inches and 5 feet 6 inches tall.

In 1986, the year Rasmussen was killed, Los Angeles recorded 831 murders, a figure nearly triple what it is today. By the end of the year, LAPD homicide detectives had solved 538 of those murders, a clearance rate of 65 percent. Of them, 463 were “cleared by arrest” and 75 “cleared other,” a catchall designation for cases in which there is sufficient information to support the arrest of a suspect but, for reasons outside police control, no arrest can be made—for instance, when the suspect is dead or cannot be extradited to Los Angeles. LAPD homicide detectives track their clearance rate the way pro athletes track their season stats. It’s the number by which their performance is judged, both within the unit and up the chain of command.

The clearance rates reported at the end of each calendar year stand in perpetuity; they cannot be “corrected” through later arrests. If a homicide occurs in late December but an arrest is made in January, credit for the clearance is taken in the year of the arrest, not the year of the murder. One corollary of this quirk is that a division can raise its current-year clearance rate by solving old cases as well as fresh ones. In 2009, for instance, the LAPD’s Olympic Division recorded seven new murders, but its detectives were able to solve a total of 15, giving the unit an eye-popping clearance rate of 214 percent.

At midnight on December 31, when the LAPD closed the books on its 1986 homicide statistics, Sherri Rasmussen’s murder was indelibly recorded as one of 293 unsolved cases.

Detective Jaramillo: Was there ever any relationship or anything that developed between you and him?

Stephanie Lazarus: Yeah, I mean, we dated.

Detective Jaramillo: Uh-huh.

Stephanie Lazarus: You know, I mean, is it—what’s this all about?

Detective Jaramillo: It’s relating to his wife.

Few people could have predicted in early 1986 that the science of police work was about to take an epochal leap forward. Not since 1901, when Scotland Yard validated fingerprinting for the purpose of criminal identification, had detectives’ power to solve crimes been so profoundly transformed.

Seven months after Sherri Rasmussen’s death, half a world away from Los Angeles, DNA was used in a criminal investigation for the first time. Two 15-year-old girls from neighboring villages outside Leicester, in the English Midlands, had been killed, one of them that summer and one three years earlier. Both victims had been raped and strangled, their bodies left beside out-of-the-way footpaths. The inescapable conclusion for both police and terrified residents was that a serial predator was hiding among the local population.

As Joseph Wambaugh, the LAPD detective turned crime writer, recounted masterfully in his 1989 book, The Blooding, an unprecedented force of 200 police officers was assembled to hunt for the murderer. Suspicion quickly fell upon a 17-year-old boy who seemed to have an unnatural interest in the second crime scene. When the boy was arrested and interrogated, he offered a rambling half-confession to the more recent murder, alternately describing his acts in great detail and then, moments later, denying he’d done anything wrong. The police were certain that he had killed both girls. But no matter how hard they pushed him, the boy refused to confess to the first murder.

By that time, police laboratories in England and America were accustomed to analyzing biological evidence, typically blood or semen, using a laboratory method called serology to determine blood type. It was useful for investigative purposes, but too imprecise to serve as a smoking gun. Serological testing that the police had expected would link the boy to the victims had come up negative, but, in light of the other evidence, they discounted the results.

Someone mentioned to investigators a newspaper article about a local geneticist named Alec Jeffreys, who had developed a novel process for mapping gene variations using DNA molecules. Jeffreys—who would later be knighted for his contributions to forensic science—realized almost instantly the potential of the new technology, for which he coined the term genetic fingerprinting. Police asked Jeffreys to develop DNA profiles from the suspect’s blood sample and from semen at the two crime scenes. The results stunned everyone. The same person had indeed raped and killed both girls. But he wasn’t the boy whom police had in custody. The first criminal suspect ever subjected to forensic DNA testing was thus exonerated by it.

The investigation went back to the drawing board in all respects except one: police now had a DNA profile of their killer, who they suspected lived nearby. In January 1987, a bold plan was announced: the police requested that all male residents between the ages of 17 and 34 provide blood samples for DNA analysis, to eliminate themselves as suspects. No one was forced to participate in “the blooding,” as the DNA dragnet came to be called, and few expected that the killer would volunteer himself. But police hoped that the list of those who declined to participate would provide new leads.

Several months and thousands of blood samples later, the police received a curious tip. A woman who worked at a bakery in Leicester had been gossiping with co-workers at a pub when one mentioned that he had agreed to take the blood test on someone else’s behalf. The woman called the police, and the naïf who’d taken the surrogate blood test promptly fingered the man who had talked him into it, a fellow baker with the improbable name of Colin Pitchfork. When confronted, Pitchfork confessed to the killings, and DNA analysis later confirmed that he had raped both girls. In January 1988, Pitchfork became the first murderer in history to be convicted on the basis of DNA evidence. All over the world, newspapers hailed the breakthrough and marveled at the ways DNA forensics might revolutionize detective work.

Detective Stearns: Had you ever met his wife?

Stephanie Lazarus: I may have.

Detective Stearns: Do you know—do you remember her name or anything or—or what she did for a living or where she worked or anything about her?

Stephanie Lazarus: Well, I think she—I’m going to say I think she was a nurse … I don’t understand why you’re talking about some guy I dated a million years ago.

Detective Jaramillo: Yeah.

Detective Stearns: Well, do you know what happened to his wife?

Stephanie Lazarus: Yeah, I know she got killed.

In Los Angeles, the first two defendants told by prosecutors that DNA evidence would be used against them promptly pleaded guilty. The third, in 1989, was an accused rapist named Henry Wilds. The prosecutor in his case was Lisa Kahn, a deputy in the district attorney’s Van Nuys office—the same branch that would have handled the Rasmussen murder a few years earlier, had a suspect ever been arrested. Wilds was charged with committing two rapes, in 1986 and 1987. The LAPD had collected semen at both crime scenes, and Kahn received permission to submit the evidence to a private lab for DNA analysis, which confirmed that Wilds’s DNA profile matched that of the rapist.

Jury selection began in January 1990. Kahn recalls her desire to find jurors who would be able to make sense of this new universe of DNA testimony. “We were looking for a bright jury,” she explains. “So I get up there first and I say, ‘Has anybody ever heard of DNA?’ Some little retired guy raises his hand and says, ‘Yeah, I know, I know. It means “Does Not Apply.”’” DNA experts testified for both sides. The jury—which included Kahn’s “little retired guy”—voted to convict. In the wake of the successful prosecution, Kahn became responsible for handling any DNA-admissibility hearing that took place in Los Angeles County.

Forensic scientists and legal historians refer to the late 1980s and early ’90s as the height of “the DNA wars.” As DNA evidence was accepted state by state, jurisdiction by jurisdiction, defense attorneys were initially helpless against the highly credentialed scientific experts called by prosecutors to testify. But that began to change in 1989, when two lawyers, Peter Neufeld and Barry Scheck, convinced a New York judge that poor laboratory procedures warranted exclusion of DNA evidence that had been introduced against their client. The decision, People v. Castro, sent shock waves through the criminal-justice system. Over the next few years, in courtrooms across America, the adversarial process worked its magic. All concerned—prosecutors, defense lawyers, forensic scientists, judges—had to raise their game. Laboratories became more careful with evidence; trial courts grew more familiar with DNA; and higher courts affirmed its admissibility as a matter of law.

By 1994, the DNA wars were basically over, as a singular case would affirm. On June 13 of that year, LAPD homicide detectives visited the Rockingham Avenue mansion of O. J. Simpson to notify him that his ex-wife and an acquaintance of hers had been stabbed to death outside her Brentwood condominium. Simpson was soon linked to the crime by forensic evidence—in particular, a blood-soaked glove that a detective named Mark Fuhrman reported finding on Simpson’s property. (Defense lawyers would later suggest that Fuhrman had planted it.) On behalf of the prosecution, Kahn coordinated the DNA testing of more than 50 blood samples that seemed to tie Simpson inextricably to the killings.

Yet contrary to expectations, Simpson’s “Dream Team” of defense lawyers did not fight to keep DNA results out, nor did they challenge the forensic value of DNA evidence during the trial. Ultimately, the not-guilty verdict turned more on Fuhrman’s alleged racism and the LAPD’s carelessness in handling evidence than on the validity of the DNA. Indeed, by the end of the trial, the DNA results had ironically become a pillar of the defense’s alternate narrative of the murder. Of course it was O.J.’s DNA: it had been planted at the scene!

By one count, the term DNA was spoken in court 10,000 times during the nine-month trial, in addition to innumerable citations on television and in print. Just five years after a potential juror had confidently informed Lisa Kahn that DNA stood for Does Not Apply, it had become a household term.

Detective Stearns: And you think—you thought—you said you thought his wife was a nurse. Do you have any idea where she was working at the time, or did he ever mention that to you? Was it a hospital or a doctor’s office?

Stephanie Lazarus: I’m sure he must’ve mentioned it. I mean, now that you’re bringing it up, I think she worked at a hospital somewhere. And, yeah, I may have met her at a hospital. I may have talked to her once or twice—

Detective Stearns: At a—at a hospital?

Stephanie Lazarus: —or more, you know?

Even as forensic technology was taking great leaps forward, the investigation into Sherri Rasmussen’s murder remained stalled. For years, her parents, Nels and Loretta, did everything possible to keep the case alive. In November 1987, they returned to Los Angeles and held a press conference, at which they renewed their offer of a $10,000 reward for information leading to an arrest. Sherri’s widower, John Ruetten, was also there. “It’s been nearly two years of hell, not knowing who did this to Sherri or why,” he told the assembled reporters. In 1988, Nels wrote a letter to then–Chief of Police Daryl Gates requesting his intervention in the case, specifically looking into the possibility that an ex-girlfriend of Ruetten’s who was a police officer might have been involved. He received no reply. About that time, Nels again mentioned the ex-girlfriend to the Van Nuys detectives. “You watch too much television,” he remembers being told.

Into the early 1990s, Loretta called the Van Nuys homicide unit regularly to inquire about Sherri’s case. In 1993, the Rasmussens traveled to Van Nuys for a face-to-face meeting with one of the detectives who had inherited the case when Lyle Mayer retired. Mayer’s successor explained that he had reviewed the original case notes and tried to advance the investigation, but he had been unable to identify any suspects, and prospects for new leads were poor. Nels brought up an article about DNA forensics he had read in a science magazine and offered to pay for DNA analysis of the evidence at a private lab. The detective turned him down. Move on with your lives, he advised the Rasmussens. After that meeting, Loretta stopping calling.

Meanwhile, in a freezer in the Los Angeles County coroner’s office, alongside biological evidence from hundreds of other murders, the swab of the bite mark on Sherri Rasmussen’s arm lay waiting for forensic science—and the LAPD’s scrutiny—to catch up with it.

Detective Jaramillo: Do you know what the circumstances were regarding her death?

Stephanie Lazarus: Geez, let me think back. Geez, I don’t know if it was—you know, if it was burglary or something. Yeah, it’s—I mean, it’s been so many years …

Detective Jaramillo: Do you remember her first name?

Stephanie Lazarus: Shelly, Sherri. I don’t know. Something …

If Lisa Kahn was the district attorney’s resident DNA geek, that role in the LAPD was filled by Detective David Lambkin. In 1981, as a young cop, Lambkin had requested assignment to the Automated Information Division, which, among other responsibilities, maintained a citywide crime database that could be searched by modus operandi or other basic criteria—for instance, all liquor-store robberies in which the suspect wore a mask. Primitive as the IBM punch-card and mainframe-computer databases might seem today, they were cutting-edge at the time, and they nurtured Lambkin’s interest in how technology could be used to solve cases. He made detective quickly and requested assignment to a sex-crimes unit. Lambkin excelled at the work, but by 1990, he felt burned out and decided to shift to homicides.

At the dawn of the DNA age, Lambkin’s background investigating sex crimes proved an excellent foundation for homicide work. Given the number of drive-by shootings then occurring in the city, LAPD detectives were far more accustomed to picking shell casings up off the street than searching for hair strands, semen stains, and other barely visible bodily traces. Lambkin, by comparison, had been working with biological evidence for years, and was already convinced of DNA’s potential. Moreover, he believed strongly that the LAPD had a moral obligation to do its best to solve cold cases. “For these families, this stuff never goes away,” he says.

In 1993, Lambkin was working homicide at the Hollywood Division, where he had a front-row seat for the conclusion of perhaps the coldest case ever solved by the LAPD. The victim, Thora Rose, had been brutally killed in her apartment in October 1963. At the time, detectives had collected more than 30 fingerprint lifts from the scene, but they had never identified a suspect. In 1990, when the lifts were uploaded to a fingerprint database, the computer reported a match with a previously unknown suspect named Vernon Robinson.

In 1963, Robinson had been an 18-year-old Navy recruit stationed in San Diego. After leaving the Navy in 1966, he fell into drugs and crime, and was eventually sentenced to three years at San Quentin for assault and robbery. Robinson emerged from prison a changed man. He got sober and enrolled in college. Later, he married and raised a family. When he was arrested for killing Thora Rose, Robinson was a 45-year-old manager for a building-maintenance company in Minneapolis. The LAPD detective who arrested him had been 8 years old when the murder occurred.

In court, Robinson cut a respectable figure. His children and members of his church packed the gallery in support of him. Deputy D.A. Paul Turley, in his closing argument, addressed head-on the defendant’s evident rehabilitation and the three decades that had passed between the crime and the trial. “I’m very happy to stand in opposition to the principle that you are entitled to one free murder every 30 years,” Turley told the jury. The jurors, and the judge, agreed: Robinson was convicted and sentenced to life in prison.

The Rose case made Lambkin eager to see how many other homicides from the city’s past might be solved using new technology. LAPD homicide detectives had always been free to work cold cases, but only as time permitted between fresh murders, which wasn’t very often. Now, using the new fingerprint and ballistics databases that had come online, Lambkin found he was able to clear some old homicides fairly easily. Although he didn’t solve every fresh case he worked, he closed enough old ones to maintain a remarkable 100 percent personal clearance rate every year from 1991 through 1996.

In October 1998, the FBI launched a DNA database called the Combined DNA Index System, or CODIS, which gave detectives the ability to compare DNA samples collected at crime scenes with the DNA profiles of legions of potential suspects. When, in 2000, a $50 million state grant became available to fund DNA testing in certain unsolved murders, Lambkin and Lisa Kahn seized the opportunity to propose a joint LAPD/D.A. task force to tackle the citywide backlog. After considerable political machinations, the LAPD’s new Cold Case Homicide Unit went operational in November 2001.

The cold-case unit initially consisted of seven detectives: three teams of two, with Lambkin at the helm. The “office” the unit was given—a 250-square-foot former janitorial storage space—was so cramped that every time someone wanted to leave, others had to pull in their chairs to make room.

The unit gradually came to grips with the magnitude of its caseload. The coldest homicide on the LAPD’s books was, literally, the first one: the unsolved murder of a man named Simon Christensen in downtown Los Angeles on the night of September 9, 1899. A century later, the unit could not do much about that one. But how far back could they go, given the inevitable loss and decay of physical evidence? “I knew from experience that there was probably nothing left from earlier than 1960,” Lambkin says. The unit’s initial focus would therefore be on unsolved homicides committed from 1960 through 1998.

Using the LAPD’s annual statistics, Lambkin tallied the numbers. During those 39 years, 23,713 murders took place in Los Angeles. Of those cases, 13,300 were cleared by arrest and another 2,668 were recorded as “cleared other.” That left 7,745 cold cases. Page by page, for months, the detectives combed the old homicide summary books. “We were looking for cases that had the best chance for us to potentially work with, given the small numbers [of detectives] we had,” says Rick Jackson, who was part of the original unit. “So we looked for sexually motivated murders, where there was a better chance for DNA. We looked at maybe a burglary murder that was unsolved. Because a burglary murder—someone is going to have broken into the place, spent some time there. In an indoor crime scene, obviously, the longer you are there, the more you do—whether you’re sexually assaulting, burglarizing, moving around ransacking—you increase the chance for good fingerprints.”

Late in 2002, when the cold-case unit finished its initial screening of all unsolved homicides committed in Los Angeles from 1960 through 1998, it judged 1,400 to have good forensic potential for reinvestigation—among them, the 1986 murder of Sherri Rasmussen.

Stephanie Lazarus: I mean, that’s—now that you guys are bringing all this stuff up, I mean, it sound—that sounds familiar. But, again, I mean, you know, what’s—I mean, what’s this got to do with me dating him and, you know, her getting killed? I mean, I—I don’t—you know, I don’t have anything to do with it …

Detective Stearns: Well, like we said, we just, literally, got this the other day … And then so, you know, I mean obviously, it’s, like—

Stephanie Lazarus: Yeah.

Detective Stearns:—we recognize the name, and we, you know—

Stephanie Lazarus: Yeah.

Detective Stearns:—you work next door to us. And so we’re trying to get some background. We’re trying to figure this out.

In February 2003, a year and a half after its formation, the cold-case unit made its first arrest, solving the 1983 murder of a young nurse and mother named Elaine Graham. A suspect, Edmond Marr, had been identified at the time but was never prosecuted; confronted with wiretap evidence and a DNA report that linked him to the murder, Marr eventually pleaded guilty and was sentenced to 16 years to life.

Seven months later, in September, the unit cleared four cases at once when it arrested its first serial killer, Adolph Laudenberg. A 77-year-old grandfather with a bushy white beard, Laudenberg was suspected of having raped and strangled four women between 1972 and 1975; the media quickly dubbed him the “Santa Claus Strangler.” The detectives possessed the killer’s DNA profile, but had no sample from Laudenberg with which they could compare it. A warrant could have forced their suspect to give them a sample, but they weren’t sure they had enough evidence to get one. They could also have asked Laudenberg to submit a sample voluntarily, but that would have alerted him that he was a suspect.

Detectives have a third way to get a suspect’s DNA sample without running afoul of the Fourth Amendment: collect a voluntarily discarded sample. In this case, it would not be easy. Laudenberg lived in a mobile home that he moved sporadically around Los Angeles. Eventually, a detective arranged to meet at a doughnut shop to discuss what he described as a series of burglaries from automobiles. Afterward, the coffee cup the old man had used was whisked to the lab and his DNA was harvested from the brim. The profiles matched, and Laudenberg is now serving a life sentence. “The press loves these cases,” Lambkin says. “I mean, it is all positive every time you solve one. If you don’t solve one, well, no one solved it. But when you do, you’re like a freaking magician.”

During the summer and fall of 2003, Lambkin’s unit was working its way, case by case, through the 1,400 unsolved homicides it had flagged as having good forensic potential. On September 19, DNA analysis was requested on evidence from the 1986 murder of Sherri Rasmussen. The request reached the desk of a criminalist at the LAPD crime lab, but given staffing shortages, no action was taken on it for more than a year.

In December 2004, a criminalist named Jennifer Butterworth noticed the unworked request sitting on her colleague’s desk and volunteered to handle it. The first article Butterworth analyzed was a blood swatch taken at the victim’s autopsy, which gave her Rasmussen’s DNA profile. When she turned to the crime-scene evidence, the items she initially tested—a piece of fingernail, a bloodstained towel—yielded only the victim’s profile. Then Butterworth noticed that the property sheet listed a bite-mark swab. Yet she couldn’t find the swab in the rape kit or anywhere else. A week went by before the coroner’s office could locate the missing evidence.

The 5-by-7-inch envelope, new and crisp when Lloyd Mahany had sealed it in 1986, was no longer so pristine. Its condition would later be described in court as “pretty beaten up” and “ratty.” There was a tear at one end, from which protruded the red-capped top of the tube holding the swab, but the tube itself appeared intact. When Butterworth analyzed the swab, it yielded a mixture of two DNA profiles, one of which matched Rasmussen’s. The other presumably belonged to her killer.

This mystery profile did not return a CODIS hit, which meant the suspect was not in the FBI’s DNA database. But a curious detail caught Butterworth’s eye. DNA profiles developed since the late 1990s typically include a gender marker. In most violent crimes, the suspect comes up XY, or male. But the DNA results in front of Butterworth were XX, meaning that the person who bit Sherri Rasmussen was female. Without the case file, Butterworth had little information regarding theories of the case or possible suspects, and so lacked context for her discovery. But it was certainly unusual. She typed up her conclusions and sent the report to the cold-case unit on February 8, 2005.

As it happened, just a few months before, California voters had overwhelmingly approved Proposition 69, a ballot measure co-authored by Lisa Kahn. Prop 69 required police to collect DNA samples from all individuals arrested for a felony or a sex crime, as well as from all state-prison inmates who had been convicted of such crimes. The DNA profiles of tens of thousands of California inmates were uploaded to the FBI’s vast database. As a result, in 2005 Lambkin’s unit was swamped with CODIS-based “cold hits”: DNA reports implicating suspects previously unknown to detectives.

As tantalizing a clue as Butterworth’s DNA report provided in the Rasmussen case—namely, that a woman might be the murderer—it did not point directly to a specific suspect, unlike the many cold hits rolling in thanks to Prop 69. Perhaps for this reason, Butterworth’s report went into the Rasmussen case file, and the case file itself went back on the shelf, where it would sit for a few years more.

Detective Jaramillo: I know you—you went to talk with her at—at the hospital regarding this issue with John to, you know, kind of like, hey, you know, what’s going to happen with this thing. But would you ever have followed up to her house where you went to talk to her to say, hey, you know what—

Stephanie Lazarus: I—I don’t even know that I knew where they lived …

Detective Stearns: But you didn’t have any issues with her; right?

Stephanie Lazarus: No, I mean, you know, obviously, if he was dating me and dating her, I probably said, hey, pick or something, you know …

By early 2007, when David Lambkin retired, the Cold Case Homicide Unit had solved more than 40 old murder cases. His successor was Robert Bub, another veteran homicide detective. Bub estimates that when he took over the unit, it numbered 10 detectives and had about 120 cases open. The team had by then moved to a new, slightly more spacious squad room on the fifth floor of Parker Center, the LAPD’s legendarily decrepit headquarters, but it still didn’t have enough space for all the murder books that it had accumulated. Detectives boxed up whichever cases weren’t being actively worked and sent them back to the divisions where they had originated, if there was room for them, or to the LAPD archives if there wasn’t.

As a result, sometime in 2007, the Sherri Rasmussen case file was returned to the Van Nuys Division in a cardboard box. By coincidence, Bub followed it in March 2008, when he accepted a transfer to run the Van Nuys homicide unit, which had just lost its supervising detective and two others to retirement. When the dust settled, the squad consisted of Bub and three other detectives: Pete Barba, Marc Martinez, and Jim Nuttall.

Whereas Van Nuys once recorded 30 to 40 homicides a year, nowadays it averages five to seven. “It’s a very manageable number of murders for three guys to work,” Bub says. In early February 2009, with the squad’s most recent homicide cleared, Nuttall and Barba began poking around for an interesting cold case. They settled on Sherri Rasmussen’s.

“It was four books when it reached me, four books deep,” Nuttall says of the case file. “They kept a pretty good chronological record of everything that was done over 23 years.” When Nuttall reached the 2005 DNA-analysis report, he saw immediately that the gender marker was incompatible with the original theory of the case. “That jumps off the page at you, because when you have that, and you’re aware that the case is based on two male burglars—well, that alters the entire course of the investigation. You have to go back to square one.”

The detectives went back over the whole investigation—but this time with the assumption that they were looking for a female suspect. When they finished going through the case file, they had a list of five names, among them that of Stephanie Lazarus, who was cited in the original police work as John Ruetten’s ex-girlfriend, with the further notation “P.O.” Nuttall didn’t make anything of the initials until he called Ruetten, who told him that Lazarus had been a Los Angeles police officer.

Nuttall was stunned at the thought that a cop might have killed someone and gotten away with it. “It was extremely difficult initially to process that possibility,” he says. Wondering whether she might still be on the job, the detectives typed her name into the LAPD’s directory, and there she was: Detective Stephanie Lazarus. Nuttall phoned Bub and told him they had identified the police-officer ex-girlfriend whom Nels Rasmussen had brought up all those years before. The suspects on the squad’s list were numbered 1 through 5. Lazarus, considered the least likely suspect, was No. 5.

The detectives on the Van Nuys squad made two pacts regarding the Rasmussen case. First, they agreed that they would maintain total secrecy, and would never speak or write Lazarus’s name where anyone else might hear or see it. There was no way to know who in the division might be acquainted with her, and they didn’t want to dirty her good name in the likely event that she didn’t have anything to do with the murder—or tip her off in the unlikely event that she did. Second, they promised one another that they would follow the trail of evidence wherever it led. “This was not a random act of violence toward Sherri Rasmussen,” Nuttall says. “Somebody on that list committed this crime.”

Stephanie Lazarus: Oh, yeah, they—my cars have been broken into, you know, but no cars have ever been stolen.

Detective Jaramillo: Uh-huh. How long—well, when—tell me about this—the car getting broken into.

Stephanie Lazarus: Well my car had been broken into several times.

Detective Jaramillo: Oh, really? Did you ever lose anything or—

Stephanie Lazarus: Yeah, now that you mention it. Let’s see. I had a gun that was stolen.

The Van Nuys detectives quickly eliminated three of the five women on their list for having insufficient motive to harm Rasmussen. That left them with only two suspects: Lazarus and one other woman, a fellow nurse who, according to the original case notes, had occasionally argued with Sherri at the hospital. “We were teetering,” Bub recalls. But as far as motive was concerned, “the information that we had was that [Lazarus and Ruetten’s] relationship had been over since the previous summer. We didn’t have anything to establish there was any animosity.”

The detectives decided they would investigate the nurse first, confirming or eliminating her as a suspect. She was located living in Northern California, and Bub made arrangements with local law enforcement to surreptitiously collect a DNA sample from her. In mid-April, just over two months into the new investigation, that DNA report came back negative. The detectives’ list was down to one name: Stephanie Lazarus.

Fact by fact, the team began piecing together Lazarus’s relationship to Sherri Rasmussen. Lazarus and John Ruetten had become close friends at UCLA, where they’d lived in the same dorm. After graduating in the early 1980s, they dated on and off. In 1985, Ruetten began dating Rasmussen seriously. He proposed to her that summer, and they married in November. Three months later, she was dead.

At the time, Lazarus was a 26-year-old patrol officer in her third year with the LAPD. In 1993, she made detective, and in 1996 she married a fellow LAPD officer, with whom she later adopted a little girl. In 2006, Lazarus was assigned to the department’s Art Theft Detail, a plum post with a degree of prestige rare for Los Angeles police work. In her long career, she had never been involved in a use-of-force incident or been accused of any misconduct.

Still, as the Van Nuys unit continued to dig, other details fell uncomfortably into place. Marc Martinez recalled that in the mid-1980s, most LAPD cops carried a .38 as their backup or off-duty gun—the same caliber weapon indicated on the ballistics report in the Rasmussen murder book. On April 30, the detectives entered Lazarus’s name into the California state gun registry, which returned a list of all the firearms she had ever registered. One of them, a .38, had been reported stolen on March 9, 1986—13 days after the murder.

Within a week, the detectives obtained a copy of the stolen-gun report. It indicated that shortly after 2 p.m. that Sunday, Lazarus had walked into the lobby of the Santa Monica Police Department, identified herself as an LAPD officer, and told the clerk that her car, parked near Santa Monica Pier, had been broken into. The lock on the driver’s-side door had been punched, she said, and a blue gym bag stolen. Lazarus listed for the clerk the contents of the stolen bag: clothes, half a dozen cassette tapes, and the handgun, which she described as a Smith & Wesson five-shot .38 revolver. Without that gun—or, more precisely, without a bullet known to have been fired from it—the Van Nuys detectives would have no way to prove, or disprove, that it was the murder weapon.

By this time, Nuttall had spoken on the phone with Nels Rasmussen, Sherri’s father, whose persistence and intelligence impressed him. “I said, ‘We need to talk about everything. I need you to walk me through everything from A to Z,’” Nuttall recalls. He asked Nels about women who might have wanted to harm Sherri, and Nels recounted what he had told detectives in 1986 about Ruetten’s cop ex-girlfriend, who his daughter said had confronted her at the hospital where she worked. Given the sensitivity of the unfolding investigation, Nuttall had to be cautious about tipping his hand. But he told Nels, “Give me time to do what I have to do, and I think I’ll be able to have an answer for you.”

Detective Stearns: Did you have a fight with her?

Stephanie Lazarus: You mean like we fought?

Detective Stearns: Yeah, did you ever duke it out with her?

Stephanie Lazarus: No, I don’t think so … I mean, it just doesn’t sound familiar. I mean—I mean, what are they saying? So I—I fought with her, so—so, now, I mean, I—I—I’m getting the jump—the leap … They’re saying, okay, I fought with her, so I must’ve killed her. I mean, come on. I mean that’s—you know, I don’t even know who those people are. I can’t even say I met any of these people. I mean, that’s—it’s insane.

If a case against Lazarus was going to proceed, it was inevitably going to end up with the department’s Robbery-Homicide Division, the elite detective unit that handles the city’s most sensitive and high-profile murder cases. Bub, a veteran of RHD, was determined to deliver an ultra-professional case to them. The detectives had known for a while that they would need to obtain a sample of Lazarus’s DNA to compare with the bite-mark swab. “We had kicked around the idea of doing it ourselves, doing surreptitious DNA,” Bub says. “But the way the circumstances were, there would have been too many variables involved and too much potential for screwup. We felt it best, if we’re going to do this and hand the package to RHD, we’re going to hand it to them with everything done correctly.”

Bub went to his lieutenant in the Van Nuys Division and briefed him on the investigation. Outside of Bub and the three men in his unit, the lieutenant was the first person in the department to learn that an LAPD detective had become a cold-case murder suspect. The captain of the Van Nuys Division and his commanding officer, the chief of the Valley Bureau, were quickly brought into the loop. “We explained that this could still turn out not to be her,” Bub says. “There were some coincidences, but there was nothing definitive for us at this point.” The chief decided that Bub’s unit could hang on to the case until the DNA sample was obtained. Back at the squad room, the detectives prepared for two possible outcomes: if Lazarus’s DNA matched the sample from the swab, RHD would assume responsibility for the case; if it didn’t match, the Rasmussen case would be designated “investigation continued” and shelved yet again, probably forever.

On May 19, 2009, the Van Nuys detectives met off-site with detectives from the LAPD’s Professional Standards Bureau, a surveillance unit directly under the command of the chief of police, who was then William Bratton. On May 27, after a week of preparation and surveillance, plainclothes detectives surreptitiously trailed Lazarus as she ran errands. When she threw out a cup and straw she had been drinking from, the surveillance team swooped in and retrieved it from the trash.

At the Scientific Investigation Division, a DNA profile was quickly developed from the saliva on the straw and compared with the unidentified profile extracted from the bite-mark swab. On May 29, Bub was on a day off when his cell phone rang. The call was from a technician at the crime lab. Bub recalls, “It was one of those gut-wrenching moments when he said, ‘Yes, it’s a match.’”

Stephanie Lazarus: I wish I had been recording this, because—because now it sounds like, you know, there’s—you know, you’re telling me these people say I’m fighting with her. And, now, it sounds like you’re trying to, you know—I’ve been doing this a long time.

Detective Jaramillo: Yeah.

Detective Stearns: We know.

Stephanie Lazarus: Okay? And—and, now, it almost sounds like you’re trying to pin something on me.

The Art Theft Detail where Lazarus worked was on the third floor of Parker Center, just across the hall from the Robbery-Homicide Division squad room. Lazarus was friendly with a number of RHD detectives, which made assigning the case a challenge. The two detectives who were ultimately chosen, Greg Stearns and Dan Jaramillo, were selected in part because they did not know Lazarus well, and had no bias for or against her. Bub says maintaining the secrecy of the investigation was a top priority. Detectives are gossipy, he explains. “That’s the nature of being a detective: we all want to know.”

Within hours of receiving the DNA results, Bub and Nuttall brought the four binders that comprised the Rasmussen case file to Stearns and Jaramillo at Parker Center. “We’re giving them this spiel of where we are and how we got here, what’s been going on for 23 years,” Nuttall recalls. “Dan and Greg aren’t asking questions yet, because they’re still absorbing this information that’s just overwhelming.” When they finished, all four detectives went straight from RHD to the D.A.’s office, where Bub and Nuttall briefed the prosecutors who would be handling the case.

To maintain secrecy, Stearns, Jaramillo, and Nuttall spent the next week working out of a conference room at the D.A.’s office. While Stearns and Jaramillo began planning their strategy for interviewing Lazarus, Nuttall and Lisa Sanchez, another RHD detective, flew to Arizona to meet with the Rasmussen family. Because many more people within the LAPD and the D.A.’s office were now aware of where the investigation was headed, concern was growing that word could leak at any moment. Nuttall and Sanchez were tasked with getting on-the-record statements from the Rasmussens and updating them on the investigation, without tipping them off to just how close the police were to making an arrest.

Despite his many phone conversations with Nels, Nuttall had never met the Rasmussens in person, and he was nervous about the encounter. The night before, and all through the morning, he went over in his head exactly what he was going to say to them: “The hardest part was, I thought, Man, Nels is going to undress this. He’s going to know I know. He’s not going to miss this.”

When the two LAPD detectives pulled up to the house, Nels came out to the driveway to greet them. The whole family was waiting inside. “He walks me in,” Nuttall recalls, “and I drew a blank on what I was going to say.” The awkward silence was broken when Loretta crossed the room to where Nuttall stood, and hugged him. “Here’s this woman who never said two words to me,” Nuttall says. “She just walked across the room and she gave me a hug.” Before the detectives left, Nuttall made one last plea for the family’s patience.

The detectives returned to Los Angeles and dove back into the case with Stearns and Jaramillo. One of the thorny issues still to be resolved was how and where to confront Lazarus. “Chief Bratton didn’t want anybody approaching her when she had a gun or access to a gun,” Nuttall explains. “There was no way anybody was going to sign off on us going into the house with a search warrant in the middle of the night and it maybe ending in tragedy.”

In the end, they decided to stage the interview at Parker Center’s Jail Division, located on the floor directly below the Robbery-Homicide Division and the Art Theft Detail. Firearms were not allowed in the jail, so it would not seem unnatural for all three detectives—Stearns, Jaramillo, and Lazarus—to surrender their guns before entering. The plan was for the RHD detectives to request Lazarus’s help interviewing a jailed suspect who claimed to have information on an art-theft case. When she arrived at the interrogation room—one equipped with recording equipment to videotape the interview—they would shift gears and gradually turn to the Rasmussen case. Given how many suspects Lazarus had arrested herself over the years, she was undoubtedly well aware of her rights to silence and to legal counsel. The unknown factor was how long she would wait before invoking one or both. “Everything I knew about Stephanie, she was sharp,” Nuttall says. Stearns and Jaramillo’s goal would be to keep her talking as long as possible, while simultaneously assuring her that she was free to leave at any time.

She would be—but only technically. As Stearns and Jaramillo would know, but Lazarus could hardly suspect, the moment she ended the interview and walked out of the room, she would be arrested, regardless of what she had told them. The interview was scheduled for early in the workday on Friday, June 5.

Chief Bratton wanted the Rasmussen family informed of the arrest in person as soon as it happened, so they didn’t hear about it through the media. Nuttall was tapped for the job. He called the Rasmussens and said he was coming back and would need to see them again on Friday morning. Nels replied that he had a doctor’s appointment. Nuttall recalls, “I said, ‘Nels, if you can reschedule it, you may want to reschedule.’”

At 6:40 a.m. on June 5, 2009, Jaramillo stopped by Lazarus’s desk. He was wearing a wire. “Stephanie?” he asked. “Do you know me? I’m Dan Jaramillo. I work over here on the other side.” He explained that he was working on a case and had a suspect in the jail who was talking about stolen art. “I don’t know a lot about this stuff,” he told Lazarus. “You can kind of talk to him. You can see if he’s for real.”

“Sure,” she said.

“Just for like five minutes or something,” Jaramillo added.

When Lazarus arrived in the interrogation room, Stearns and Jaramillo abandoned the story of a suspect talking about stolen art, and explained that her name had come up in a case involving an ex-boyfriend of hers, John Ruetten. Knowing she was married to someone else, they told her, they’d selected a place where they could speak privately, away from gossiping colleagues.

Stearns and Jaramillo interviewed Lazarus for more than an hour, coming at her in an oblique manner that left it unclear whether they were speaking with her as a possible witness or a criminal suspect. The conversation meandered, but every digression led back, inevitably, to the murder of Sherri Rasmussen. It was only after Jaramillo asked Lazarus if she’d be willing to give them a DNA swab and noted, “It’s possible we may have some DNA at the location,” that she said she wanted to contact a lawyer. Declaring herself “shocked,” the veteran detective stood and walked out, 68 minutes after she’d sat down. Lazarus got only as far as the jail’s hallway, where she was stopped by other RHD detectives and placed in handcuffs.

Unidentified Speaker: Too tight? … Which one, left or right?

Stephanie Lazarus: You know, it’s the left but that’s—you know, I think it’s just … hitting my watch.

Unidentified Speaker: Yeah. You want me to take your watch off? They’re going to take it off anyway. Property bag?

Stephanie Lazarus: Well, just—

Detective Stearns: Yeah, just put it in here … Go ahead and grab her ring, too. Want to stand up for just a second?

Stephanie Lazarus: Oh, geez. See if I can get it off.

Detective Stearns: Okay.

Stephanie Lazarus: I’m going to probably have to lick my finger … I need a little spit.

[Lazarus and the detectives discuss other topics for a while—a torn ACL she suffered playing basketball, medication she needs to take every morning—before returning to the ring.]

Unidentified Speaker: They already—they still have your property over there, if you want to take your ring off … Saliva works wonders.

Stephanie Lazarus: Yeah.

From the interrogation room, Lazarus was taken to Lynwood, the Los Angeles County jail facility for female prisoners, where she has been held ever since on $10 million bail. On June 8, 2009, she was charged with the murder of Sherri Rasmussen. Since her arrest, Lazarus has steadfastly maintained her innocence. Through her lawyer, she declined The Atlantic’s interview request. Her trial is tentatively scheduled to begin in late August.

Video: Watch key moments from Lazarus's interrogation

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