In August 2007, Michael Vick pleaded guilty to the case that jettisoned him from celebrity into notoriety. The Atlantic Falcons quarterback’s dogfighting ring had been exposed in such graphic and shocking detail that his coterie of star defense attorneys panicked, then folded.

The person who dug up this hard evidence against Vick—by literally exhuming the bodies of dead fighting dogs and proving they’d been hanged—was Melinda Merck. An ace at forensics, Merck has helped crack cases involving crimes from pedophilia to drug dealing. She’s credited by the chiefs of both the FBI and the National Sheriffs’ Association with having revolutionized their crime-fighting efforts, and won awards from both the Department of Justice and the U.S. Office of Inspector General.

But Merck isn’t a run-of-the-mill crime-scene investigator. She’s a veterinarian.

For more than 20 years, Merck has been studying and solving animal-abuse cases. Now, she’s going a step further by persuading law enforcement that there’s a link between animal cruelty and other serious crimes, like domestic violence, arson, and murder. It’s CSI for animals, but with a twist: Look closely, says Merck, and you’ll likely find a clue that leads to a whole trail of criminal behavior.

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In 1990, Merck discovered what she now refers to as “the dark side.” While she was a feline specialist at a veterinary practice in Atlanta, a couple turned up with a kitten that they claimed had injured itself under a kitchen cabinet. Merck’s examination determined otherwise: The kitten had been beaten. She called the police, and within a week, the couple was charged with animal cruelty.

Officers told her they’d never heard of a vet reporting suspected abuse before, which surprised her. “Vets are natural detectives,” she says. “We have to figure it out every time a patient comes in with clues from the animal, our diagnostics, the owner.”

Nevertheless, according to Merck, her boss at the practice was less than thrilled by her sleuthing. The law doesn’t require vets to involve themselves or the police in suspected animal-abuse cases, and doing so risks alienating some pet owners. Merck knew she had to quit. “There’s a moral aspect to being a vet that is more important than whether or not a bill is going to be paid,” she says. She set up her own veterinary practice.

A year later, a distraught woman showed up with a dog that had been stabbed by her boyfriend, Merck says. Once again, she alerted the authorities. But this time the behind-closed-doors scene was more complex. When the police questioned the couple, it emerged that the dog wasn’t the only victim of abuse in the household. The boyfriend was arrested for domestic violence against his partner.

That was Merck’s light-bulb moment—the moment the dark side became clear. “People who commit animal cruelty are usually criminals in other ways,” she realized.

Eager to determine just how strong such an association might be, Merck embarked on a 15-year quest to learn everything she could about forensics. On top of running her practice, she spent her spare time traveling around the country to participate in classes like “Death-Scene Investigations in the Natural Environment,” “Gunshot Reconstruction,” and “Death-Scene Checklist.” When she enrolled in a bloodstain-patterns course in New York, she was the only non–police officer there. Over time, she learned how to take DNA swabs, how to use a blue light to reveal whether bloodstains are from humans or other mammals, and how to photograph crime scenes.

By 2009, Merck was armed with the kind of arsenal of forensic knowledge one would normally only associate with law enforcement. She left her practice to set up an animal-forensics consultancy in Austin. In partnerships with the American Society for the Prevention of Cruelty to Animals (ASPCA) and the Animal Legal Defense Fund, she began persuading police officers and attorneys to rely on her unusual expertise. “It’s foreign to them, what the medical records, what the words, the abbreviations, the exam, or necropsy findings mean,” she says.

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Until recently, animal cruelty was categorized as a simple misdemeanor, not an indication of a perpetrator’s likelihood to commit other crimes. But research over the past few decades increasingly has backed Merck’s conviction. Back in 1986, a study in the International Journal of Law and Psychiatry found that almost half of rapists and a third of child molesters reported committing animal abuse during childhood or adolescence. In 2001, the U.S. Department of Justice’s Office of Juvenile Justice and Delinquency Prevention reviewed the existing research and determined that nearly two-thirds of inmates who commit crimes of aggression might also abuse animals.

More recently, a study by the Chicago Police Department “revealed a startling propensity for offenders charged with crimes against animals to commit other violent offenses toward human victims.” A survey of women in domestic-violence shelters indicated that 71 percent had partners who abused or threatened to abuse pets.

These studies don’t imply that all people who harm animals are hiding other crimes, nor do they suggest that a first-time animal abuser is destined for a future of malfeasance. Nevertheless, Merck takes the results to mean that abuse cases do deserve closer scrutiny than they’ve traditionally received from law enforcement. Animal abuse used to be lumped into an “All Other Offenses” category in the FBI’s National Incident-Based Reporting System, the database law enforcement uses to store and compare records on all serious offenses. But by 2015, after Merck and animal charities began lobbying, the initially skeptical agency started to look at animal cruelty as a tool for detecting or proving other crimes. Last January, the agency elevated animal cruelty to its own category in the system, to be tracked alongside crimes such as homicide and arson. (Data will be published later this year for the first time.)

John Thompson, the deputy executive director of the National Sheriff’s Association, is the one who convinced the FBI to reclassify animal cruelty last year. The ASPCA had persuaded him to look at the evidence. “I put my hands up. I spent 35 years in law enforcement and couldn’t have cared less about animal abuse,” says Thompson, who sits on the FBI’s policy advisory board. “I was stupid. No one was educated. It’s how we used to think about domestic violence: ‘If a woman is getting beaten up by her husband, why doesn’t she just get out of the house?’”

Thompson points to the case of Alexander Hernandez, who was arrested in California in 2014 for shooting a dog—a crime that might in some states pass as a misdemeanor or criminal damage and not become grounds for further investigation. But when the police ran ballistics on Hernandez’s gun, they identified him as the man behind a series of murders.

“Eighty percent of law enforcement still doesn’t know about that link, but once you show them, they get it right away,” Thompson says. “It’s huge. The more people know about it, the more crimes we’re going to solve.”

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Merck hasn’t won everyone over, however. Her approach can be controversial, especially among more traditionally minded vets and judges and juries who aren’t as willing as she or Thompson are to make “the link.”

A danger of veterinary forensics, as critics see it, is wrongful conviction—the possibility that too much is read into an alleged abuse case, and a person gets accused of a crime they didn’t commit. This came up in 2009, in a case centered around Tyler Weinman, a high-school senior living in Florida. It was reported that Merck, a key state witness, had confirmed that Weinman was a serial cat killer, though she never personally inspected the carcasses. Weinman was vilified in national headlines, but the case fell apart when the defense produced evidence that several of the cats had most likely been killed by dogs.

Soon, Merck came under scrutiny again when she determined that a 65-year-old businessman named Armand Pacher had intercourse with his Great Dane. Pacher was arrested based on Merck’s findings, but a judge determined that Merck lacked credibility after four board-certified mammalogists questioned her analysis. She “made false statements in this report in order to exaggerate the true facts,” one of the experts, the animal-reproduction specialist Bruce Eilts, concluded. All charges against Pacher were dropped.

In response to the Weinman case, Merck argues that she was brought in too late, and that she had never personally alleged she’d found evidence of human-caused mutilation. “Since then, I have testified in the related civil case against the county and there have never been any charges against me,” she says. She also points out that, in the Pacher case, Eilts and the other experts had no formal training in veterinary CSI.

Both cases affected the credibility of the field of veterinary forensics, though forensics vets I spoke to unanimously supported Merck and maintained that even accurate forensics analysis can be eviscerated in court by a good defense lawyer. Multiple forensic-science institutes also vouched for the legitimacy of her approach. Merck herself remains staunchly defensive of the profession’s mission: “We are veterinarians who are applying medical and scientific knowledge to answer legal questions in animal cases,” she says. “As long as it is done objectively and with the proper experience and training, the testimony speaks for itself.”

Or, as she also told me: “Not every vet can cope with the dark side.”

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The case that cemented Merck’s reputation as the go-to expert on veterinary forensics came to a head last year. Wilson Longanecker Jr., the young mayor of Sorrento, Louisiana, was beloved for adopting a number of kittens—but then police discovered indecent images of children on his computer, along with other pictures that showed what had happened to the cats. When Merck established that Longanecker had tortured them after adopting them, the mayor agreed to a plea bargain. He’s now one year into a 40-year jail sentence.

“No matter what the other crimes are,” says Merck, “perpetrators know that the animal cruelty is not going to play well with the jury or the public. The victim is helpless and defenseless.”

Animal abuse is beginning to be interpreted as the first outward sign of distress in a household (a child who hurts animals may be acting out scenarios they’ve encountered at home), but remedial work is only slowly starting to proliferate. Some schools include “humane education” on their curricula, designed to teach children empathy. There’s only one nationally recognized cognitive-behavioral intervention for child animal abusers: Based on psychodynamic and attachment theories, AniCare is meant to help perpetrators accept responsibility for their actions and respect for animals. Judges in seven states have specified AniCare Child in sentencing.

As Merck sees it, there’s still a lot of work to do. She’s currently part of a push to make sexual abuse of animals illegal in Texas, which is one of eight states that doesn’t ban bestiality. The campaign had new life breathed into it earlier this year when a deputy sheriff, Andrew Sustaita Jr., was found to have more than 200 indecent images of children on his personal computer as he was being investigated for allegedly posting a video online of himself having sex with a small dog.

Laws against cockfighting and other forms of animal abuse remain lax in some states, and education about animal cruelty is not a mandatory part of police training (officers can choose to take it as a module). Tennessee and New York City have introduced public registries of animal abusers, but farming lobbies in other parts of the country fear that such legislation could snowball into an unwelcome tightening of all the laws around keeping livestock or lead to the false incrimination of farmers who use artificial-insemination techniques. Some hunting and farming lobbies would prefer the ban on sexual abuse of animals to apply only to pets.

Veterinary forensics can come off as quackery to people who are new to the concept. Still, Merck expects to see special animal-cruelty courts set up within the next decade. Thompson, the National Sheriff’s Association deputy director, for his part, thinks it will take longer to convince the public that there’s a link.

“I feel positive that attitudes are changing, but people can be stubborn,” he says. “We need to take animal cruelty seriously if we’re going to start solving other crimes—but it took me 20 years to accept that.”