The 17-year-old who killed 10 people at Santa Fe High School, in Texas, allegedly used his father’s shotgun and .38 revolver. After a firefight with police, he surrendered, saying he did not have the courage to kill himself, as he had planned, Governor Greg Abbott told reporters.

In the hours after the May 18 attack, some students were shocked that Dimitrios Pagourtzis felled his classmates and two substitute teachers with buckshot. He played defensive tackle on the football team. He made honor roll. He is not known to have a criminal record, according to Abbott. Just the day before, he had been joking around with friends on a field trip to a waterpark. Others found him disturbing, often wearing a trench coat, said his classmates, and, on that day, a black T-shirt with the haunting message BORN TO KILL.

Details are only beginning to emerge about the gunman, and now it seems he kept his plans to himself, described in his personal journal. This would be unusual. In many of the other 21 (by CNN’s count) school shootings this year, there were clues to what would come to pass, to varying degrees. Typically, someone—a parent, a classmate, a teacher, a neighbor—had a hunch as to what would happen. Sometimes it was clear the child was mentally ill. Sometimes he had overtly displayed psychopathic traits. Sometimes other students steered clear of that particular boy at lunch in the hallway, because he was just plain scary. As Mary Ellen O’Toole, a retired FBI agent who’s an expert on school shootings, notes: “They never come out of the blue.”

If the clues were there, couldn’t these teens have been stopped? Faced with a dangerous child, families, schools, and police can do their utmost, and their utmost frequently staves off tragedy. But events like this point to a discomforting reality: Even though many potentially violent children can be treated and do get better, it’s impossible to ensure that every dangerous child will be reached. And, in the end, there’s not much that anyone can do to stop a determined shooter, aside from preventing him from getting a gun in the first place.  

* * *

The first line of defense is the family, the parents and siblings who know that their boy—and it’s almost always a boy—just might be an unpinned grenade. When researching a story for The Atlantic on deeply troubled children, I was struck by how terrified and helpless these parents felt. One of those parents, Liza Long, told me she vividly recalls the moment she learned of the shooting at Sandy Hook Elementary School in Newtown, Connecticut, when a young man named Adam Lanza took his mother’s semiautomatic weapons and killed 20 children, six adults, and himself. “My first thought,” she says, “was: What if that’s my son someday?”

Long’s son, Eric, displayed many of the signs of a future shooter. His violent eruptions began early, in kindergarten. Long’s other children knew that if she yelled “Safety Plan!” they were to run to the car, lock the doors, and call their father and the police; Eric’s teacher also developed a protocol to evacuate the other children whenever he melted down. By 13, Eric had been expelled from school and sent to juvenile detention four times.

A few days before the Sandy Hook shooting in December 2012, Liza Long made a request both mundane and nearly fatal. She asked her son to return his overdue library books. “And literally within 60 seconds, I had a knife at my throat,” recalls Long, who also describes her son’s illness in her book, The Price of Silence. “And the really sad thing was: This was normal.”

Here is the first hole in the first line of defense: Denial. Parents are often confused and overwhelmed by their child’s behavior, but they grow used to it, tolerate it, adjust their lives around it, and attempt to cope with it alone.

This seemed to be the approach Nancy Lanza adopted, as she watched her son spiral into a struggle with mental-health issues: depression, anxiety, and obsessive-compulsive behavior. Nancy, who was Adam’s first victim, has been blamed for dismissing repeated suggestions by schools and by psychiatrists that Adam needed therapy and medication. Instead, she took him out of school and let him spend his days and nights in his bedroom or in the basement, where police reportedly found a large-format spreadsheet listing some 500 large-scale killings and the weapons the perpetrators used. (Afterward, a state investigation concluded that mental illness alone did not lead to Lanza’s “murderous acts.” Rather, “his severe and deteriorating internalized mental health problems ... combined with an atypical preoccupation with violence... [and] access to deadly weapons ... proved a recipe for mass murder.”)

But even parents willing to hospitalize their mentally ill child may run into problems. They have surprisingly few options when faced with a dangerous son or daughter. For older kids—it varies from state to state, but generally the minimum age is 15—the child must have made an overt threat that he might harm himself or others. He may have an explosive temper; he may even have access to guns. “But if he hasn’t come right out and said, ‘I’m going to kill someone tomorrow,’ or ‘I’m going to kill myself,’ you're not going to be able to involuntarily hospitalize him,” says Michael Caldwell, a psychologist at the University of Wisconsin who works with dangerous young men at a juvenile treatment center in Madison.

A parent of a child 14 or younger can legally commit him to a mental-health facility without an overt act—but generally, only for three days. And here, there is a practical problem: scarcity of treatment. Liza Long says that after Eric put a knife to her throat, he was taken to the emergency room, where they administered a drug to calm him down. Then the hospital informed her they had no beds for him in the psychiatric hospital. In fact, Eric’s social worker told her the only way to get Eric the mental-health services he needed was to press criminal charges against him. “So those were my options,” she says. “‘We have no idea what’s wrong with your kid. We think he needs a psychiatric bed, but there’s nothing available. Here’s a drug that will knock him out.’” She took him home with a prescription for an antipsychotic drug called Zyprexa.

Caldwell hears this all the time. “Twenty-five years ago,” he says, “if you had insurance, you could probably get the kid put into a psychiatric unit for 30 days for an evaluation and try to get a handle on what's going on. Those beds have just disappeared.”

Aside from the practical, legal, and emotional barriers—after all, who wants to commit their child?—parents have another incentive to keep their secret close, as Nancy Lanza did: fear of losing her other children. Several specialists and parents told me that social workers often believe that a child’s erratic behavior stems from abuse in the home. One woman with a violent daughter described how the local Child Protective Services department accused her and her husband of beating their daughter and depriving her of food. The agency threatened to take away their other children and investigated the parents for a year before determining there was no abuse. For her part, Liza Long lost custody of her two younger children after she published a heartfelt blog post headined “I am Adam Lanza’s Mother.” After the essay spread online, the judge granted her ex-husband full custody of the two children if she insisted on raising Eric. “Why won’t families talk about this?” Long asks. “That’s why.”

Experts stress that children with mental-health problems are no more likely to be violent than other children. Even if mental illness is a reason behind some of the mass shootings, Long says, “I have great news for you. Treatment actually works. All you’ve got to do is give people access to services.” Once her son was correctly diagnosed with bipolar disorder, the medication kicked in, and the violent eruptions ended. He is flourishing. Next year, he is heading to college on a full scholarship.

If a child with obvious mental illness presents an agonizing dilemma for parents, an apparently sane but violent child poses another set of legal questions. For example, experts are divided over whether Nikolas Cruz suffered from severe mental illness when he allegedly killed 17 people with an AR-15 semiautomatic rifle at Marjory Stoneman Douglas High School in Parkland, Florida in mid-February. But many people who knew him—family, classmates, teachers, neighbors—believed he was a budding criminal. He was violent, obsessed with guns, cruel to small animals. Cruz’s mother regularly called the Broward County police to come talk to her son. In fact, local police received some two-dozen calls about Cruz. A woman who knew the young man called the FBI five weeks before his attack and told an agent that Cruz owned a gun; she worried that he was going to “explode” and go to a school, “shooting up the place.”

In nine states, these warnings would probably suffice to let police confiscate his guns. Under so called “red flag laws,” a family member, friend, or police officer may ask a judge to issue a “gun violence restraining order” against someone who is considered dangerous to himself or others. If that request is granted, police can seize the guns immediately. Typically, the order expires in one year, but it can be extended if a judge believes the person is still dangerous. At the time of the Parkland shooting, Florida did not have a red flag law; one has since been enacted.  

The other option—detaining a young person who seems dangerous—is even trickier. “This is not Minority Report,” says Marsha Levick, the chief counsel at the nonprofit Juvenile Law Center, referring to the sci-fi movie in which the government can foresee crimes and arrest would-be wrongdoers before they act. “We don’t arrest people for what they’re thinking. We arrest them for what they’re doing.” Individual thought is beyond policing, and the Constitution protects speech, but determining when speech tips from repugnant to criminal isn’t always clear. People were shaken by Cruz’s behavior and his posts on the Instagram and YouTube. But at the time, did his contributions to social media merit his arrest? It’s easier to answer that question in retrospect than in the moment.

This all points to the tough knot at the center of these questions: Of course, the vast majority of children post or say threatening things and never act on them. Even the most severe behavioral cases—children exhibiting psychopathic tendencies—usually grow out of their scary behavior as they pass through adolescence. This is one of the greatest dilemmas of psychologists and parents: How can they possibly tell in advance who is a real threat and who isn’t? How can you tell apart an Eric Long and an Eric Harris, one of the Columbine shooters?

* * *

And what if parents see no indication of violent ambitions? What if neither mental illness nor seething delinquency hints at the disaster to come? What if you are Sue Klebold? Her son, Dylan, partnered with his best friend, Harris, to kill 12 classmates and one teacher at Columbine High School on April 20, 1999, before killing themselves. Columbine was breathtaking not only for the number of fatalities but its exquisite planning and cold execution. Yet for the family on the first line of defense, there had been few red flags.

At the time, Sue Klebold saw nothing particularly alarming about her son. As she wrote in her book, A Mother’s Reckoning, she knew her son was often “crabby” and sometimes withdrawn. She was angry when he and Eric Harris broke into a van in their junior year, but that was his only brush with the law. Dylan had friends, he watched old movies with his parents, he went to his senior prom, he was headed for the University of Arizona. “Things have been really happy this summer,” Sue Klebold wrote in her journal in July 1997, the summer of Dylan’s sophomore year.* “Dylan is yukking it up and having a great time with friends.” She didn’t know that Dylan had been contemplating suicide for months, that he wrote in his own journal that very same month, “i feel so lonely, w/o a friend.” He drank heavily; by senior year he was stockpiling weapons, making videos and plotting a massacre with Harris. (Eric Harris’s family has never spoken publicly, so it isn’t known what clues, if any, they spotted.)

O’Toole, the former FBI agent and director of George Mason University’s forensic science department, says that even though it takes time for kids to morph from troubled and nonviolent to a mass shooter, this “self-radicalization process” can be hard for parents to detect. Harris and Klebold spent more than a year plotting the locations and timing of the attack, learning how to build bombs and buying semiautomatic weapons before they went through with their plans. “The planning can make them feel powerful,” says O’Toole, who headed a team of FBI and academic experts that examined school shootings. She notes that this planning phase can be easy for parents to miss. “They’re a little bit happier than they were before. They’re more self-assured, and they’re enjoying the planning part of it.”

Psychiatrists and profilers who have studied Columbine seem to agree that that Eric Harris was the charismatic leader and Dylan Klebold was the shy follower. Harris tilted toward psychopathy while Klebold tipped toward depression. “I am a gun,” Harris wrote in his journal. “I was never made for hunting, just for killing humans.” Klebold wrote of suicide and unrequited love for a girl, of his “infinite sadness, I want to find love.” During the massacre, Harris shot liberally, Klebold sparingly. Harris taunted people between rounds, telling one girl who was groaning in pain: “Quit your bitching.”

Children who are callous and unemotional—which is how psychologists refer to young psychopaths—comprise about 1 percent of the population of children, and most of them grow into fairly well-adjusted adults. Some do not—and those who don’t account for about half of all violent crimes, according to multiple studies and experts I have spoken with. Many of the shooters with the highest body counts—Klebold and Harris, Lanza, and several others—seem to have come from stable middle-class households. In fact, the vast majority of school shooters come from two-parent homes and have clean arrest records. They’re not habitually violent nor part of a gang. According to an assessment by the Secret Service, in seven out of 10 cases, they are the bullied victim, not the original aggressor.

In the deadliest school shootings since 1999, the first line of defense—the family—failed. The Klebolds saw no red flags—not contemporaneously, anyway. Adam Lanza’s mother sheltered him from the outside world as he burrowed deeper into illness. Nikolas Cruz’s mother was well aware of her son’s delinquency, but as often as the police visited their home, he was never arrested.

Usually, the first line of defense holds—most parents see warning signs, and get their children the treatment they need. But it’s the exception to this that ends tragically.

* * *

What about the second line of defense—schools? After the shooting in Parkland, Florida, President Trump and others demanded that schools make themselves “harder” targets. They recommended (among other things) arming teachers, hiring more on-campus police, installing more metal detectors, and screening the bookbags and handbags of students and visitors as they enter the school. After the shooting at Santa Fe High School on Friday, Texas’s Lieutenant Governor Dan Patrick suggested that the incident might have been avoided if the school had had only one entrance.

Classmates, teachers, and in-school police officers may be better positioned than families to spot a troubled kid, since they are not as blinded by affection or genes. But hardware upgrades won’t stop a committed shooter, says Ronald Stevens, the executive director of the National School Safety Center, an advocacy group. Consider Adam Lanza, who killed 26 people at Sandy Hook Elementary School. “They had metal scanners, camera surveillance, perimeter controlled, visitor screening, fencing—you name it,” Stevens says. “The guy still came in, and he managed to overpower those at the entrance and then get on to campus.”

Rather, he and many experts believe schools should focus more on prevention than on security. This is not a new idea. After the Columbine shooting in 1999, government and academic researchers closely studied some three dozen attacks at schools, with one central question: How can they predict, and thwart, future attackers long before they walk into the building?

Answering that question is difficult for much the same reasons that parents can have a hard time knowing whether their child's behavior indicates merely a short-term problem or something much graver. The researchers compiled a list of characteristics and behaviors that many of the shooters shared, and concluded, “there was no single profile of these kids that would be scientifically reliable,” says Dewey Cornell, a psychologist at the University of Virginia who worked closely with the Secret Service and the FBI. “People say, ‘Well, these kids are victims of bullying, these kids are paranoid, these kids play violent video games, these kids are narcissistic.’ And many of the kids who have committed school shootings have those traits. But so do a million other kids. And this is a problem of specificity—that is, you find characteristics, but they're not specific enough to be useful.”

The answer to that question—to identify a threat early, assess its severity, and then thwart the perpetrator’s plans—became all the more apparent in 2007, when Seung-Hui Cho, a senior at Virginia Tech, killed 32 students and wounded 17 others. An examination after the tragedy found that Cho had serious mental-health problems that went untreated. Before the shooting, a counselor had found him to be a danger to himself and others, and recommended involuntary hospitalization. That didn’t happen, and Cho’s case fell through the cracks of a school counseling system in disarray. The clues were there long before he turned violent.

After the shooting, Virginia’s legislators realized that schools needed to act early, spotting the first symptoms of distress before they had a chance to bloom into rage, psychosis, and ultimately homicide. Across the country, districts set up “school assessment” programs, which, like Virginia’s, often involve administrators, counselors, school police officers, and teachers.

The programs work like this: When a school becomes aware of a threat, the team rates its severity. If the kid is spouting off in a moment of anger, which is usually the case, the school can counsel him and move on. If the threat seems more severe—if it’s specific, or shows evidence of planning, or suggests the boy has access to weapons—then the school develops a more elaborate plan. School officials may meet with the young man “to let him realize that he’s being monitored,” says Cornell. Schools can offer mental health services to the boy—although generally, the school cannot have a child committed without the parent’s permission. They can look at court records for evidence of past violence. They can also search for weapons in the school.

All the while, the school keeps tabs on the boy, looking for changes in behavior: Are his grades suddenly slipping? Is he coming to school disheveled? Is he more aggressive? Does he isolate himself at school? Does he spend all his time in his room at home, refusing to come out for dinner? “These behaviors are evolving,” O’Toole, the former FBI agent, says. “For example, it’s not just that he’s fascinated with guns—but now he’s actually amassing guns.”

Many people knew that Nikolas Cruz was amassing guns over the year preceding the Parkland shooting, and said so. But long before that, back in 2012, when Cruz was 13, his middle school knew he was in need of help. He was counseled. He got in fights and swore at teachers and classmates. In January 2017, Marjory Stoneman Douglas High School asked the school board to conduct a threat assessment, although it’s not clear that happened. Finally, on February 8, 2017, Cruz was transferred from the school. Three days later, he bought the AR-15 that he would use to kill his classmates a year later.

This might have been a misstep on the part of the school. Once Cruz was transferred from the public high school, the system lost track of him. He attended three alternative schools for at risk youth, including The Off Campus Learning Center, the Henry D. Perry Education Center, and the Dave Thomas Education Center. “You just don’t want to have him out of sight, out of mind,” Cornell says, “because some of them come back with a gun.”

Cornell’s point stems in part from a surprising pattern that O’Toole’s FBI research group had found: The shooters often had tipped people off. “It was called ‘leakage,’” O’Toole says, “like a leaky faucet.” And it seemed to be a regular behavior of school shooters.

According to Jeff Daniels, a professor of counseling at West Virginia University who has studied school shootings, the FBI has found that in four out of five cases, the shooter told someone about his plans or revealed his intentions on social media. “This is where kids in mass shootings are a little different from adults,” Daniels says. “Developmentally, adolescents want to draw that attention to themselves even beforehand. Most adults that go on a shooting spree don't do that.”

Even in the most notorious high school attacks, the shooters were leaking their intentions: Dylan Klebold and Eric Harris produced a video for class in which the two young men, wearing trench coats, portray themselves shooting several people at school, before setting off pipe bombs. Klebold also wrote a short story, in which a man dressed in black attacks popular kids at school; the story prompted his teacher to speak to his parents.

Adam Lanza confided to one man that he had an assault weapon and planned to kill children at Sandy Hook Elementary School; the man told the local police. Another woman who communicated with Adam online told the FBI after the shooting that he spent time researching mass murders and killing sprees.

As an English major at Virginia Tech, Seung-Hui Cho’s behavior and violent writings worried his professors, according to a state investigation. One feared for her safety. Another described a work of short fiction in which Cho’s protagonist plans a mass school shooting.

Nikolas Cruz posted so many alarming statements on the internet, including his desire to be a professional school shooter, that “I’ll call that one gushing, rather than leaking,” says Daniels. “He definitely let people know his intentions. He was on multiple radars.” And yet Cruz, like the others, was able to carry out his plans.

Daniels adds that the schools can develop another key information source: the kids that attend classes with a possible assailant. He says more shootings have been thwarted than accomplished, often because a classmate spoke up. Daniels, who studies foiled plots, recalls the case of a middle-school student who overheard two brothers talking in the bathroom, and heard one say, “I have the gun.” The boy found a school counselor, who alerted an on-campus police officer, who approached the would-be shooter just as he was reaching into his backpack for his gun.

A critical change schools can make, which avoids the complexities of calling the police or trying to hospitalize a student, is cultivating trust with these young witnesses. Kids know who’s bringing knives and guns to school. The students in Parkland knew to steer clear of Nikolas Cruz. “Students being eyes and ears is critically important,” Daniels says, “and when they hear something or see something, to be able to come forward and talk about it and tell an adult.” The successful schools try to emphasize that there’s a distinction between snitching and getting help. In one school Daniels studied, the teachers eat lunch with the kids in the cafeteria. “The principal said, ‘You’d be amazed at the kinds of things that kids tell their teachers when they know them on a more personal level.”

Ronald Stevens, of the National School Safety Center, argues that schools also should be more proactive in sharing their concerns with outside authorities. He recognizes that schools have an obligation to protect children's records and privacy, and that the Constitution protects their speech—but he worries the pendulum has swung too far—risking the safety of classmates and teachers. “Wouldn’t you want to know if Charlie Manson Jr. had just been assigned to your school?” he asks. “Let’s broaden the net,” he says. “Let’s bring in the juvenile and family court judge, let’s bring in probation, let’s bring in Social Services—a whole network of people that have got to start working together more carefully.”

When the actions of the parents, neighbors, and school fail, there remains one last backstop: The state.

As mentioned above, some states have red-flag laws, which allow police to temporarily confiscate guns from a person who is believed to be a danger. Moreover, under federal law and some state laws, states can arrest and prosecute a person for making “terroristic threats.” But these are hard to assess, says Marsha Levick at the Juvenile Law Center: What is a terroristic threat? Levick says that it’s a statement intended to cause fear or harm. “But where does one draw the line?” she asks. Was Nikolas Cruz’s social-media post saying he aspired to be “a professional school shooter” dangerous or specific enough to have him arrested? Or his Instagram pictures of slaughtered frogs, and his writing, “I want to kill people”? With perfect hindsight, Levick says, there was a pattern of threatening behavior that may have met the standard. But viewed individually, even those warning signs might not trigger an arrest.

As for other school shooters, including the assailants at Santa Fe, Columbine, Sandy Hook, and Virginia Tech, the police had no grounds for arrest, since they had not made specific, credible, and imminent threats.  

* * *

Virtually everyone I spoke with, from the FBI to academic researchers, told me it’s nearly impossible to stop a determined shooter; they’re always one creative step ahead. In one way, Dimitrios Pagourtzis broke with recent shooters: He used his father’s shotgun, rather than a semiautomatic weapon—although Pagourtzis made the shotgun far more lethal by using buckshot. In other cases—at Stoneman Douglas High School in Parkland, Florida; at Virginia Tech; at Sandy Hook Elementary in Newtown, Connecticut—the gunman used a semiautomatic weapon to wreak even more carnage. Stopping a young person from stealing his parents’ legally owned shotguns is impossible; but experts like Michael Caldwell say that restricting the sale of semiautomatic weapons would go some way to limiting the carnage.  

“It may not decrease the number of incidents, but it would decrease the number of fatalities,” says Michael Caldwell, the University of Wisconsin professor, not just because he can get off fewer rounds, but because bullets fired from an AR-15 are so much more lethal. “You don’t have to hit the target straight on to kill a person. If you’re shot in the torso, it will kill you.”

One study tracked school shootings in three dozen countries—incidents in which two or more people died. Half of those shooting incidents occurred in the United States. Given that, according to some studies, Americans are no more emotionally troubled than people in Europe and Canada, the stark difference is guns. Children outside the U.S. “don’t have access to AR-15s or Glocks or other weapons that our kids have access to,” says Dewey Cornell. “That’s a huge glaring obvious problem. It’s obvious to scholars in the field. It’s obvious to folks in other countries. For some reason it’s not obvious to our politicians.”


* This article originally misstated the year of Sue Klebold’s journal entry. We regret the error.