If a threat is not a crime, can the police prevent a school shooting?

Miami: Last year, when an investigator from the sheriff's office in Jackson County, Georgia, interviewed a 13-year-old and his father about a possible online threat to "shoot up a middle school," the teen denied responsibility.

I have to take you at your word, the investigator, Dan Miller, told him, "and I hope you're being honest with me."

Nearly 16 months later, police say that the teenager, Colt Gray, who is now 14, killed four people and injured nine others at Apalachee High School in Winder, Georgia, on Wednesday. It was the deadliest school shooting in the state's history.

Could law enforcement officials have done more to prevent it?

The painful and inevitable question has frequently dogged police after shootings. Experts say that most mass shooters display warning signs before becoming violent, and officials have often received tips, calls or reports about concerning behavior -- sometimes long before someone picks up a weapon.

But law enforcement officers, at least under traditional police training, are limited in what they can do in response. If a crime has not been committed or a subject does not meet the criteria to be sent for an involuntary mental health evaluation, the case is often closed.

"It's easy in hindsight to say, 'Well, they should have done more,'" said Adam Winkler, a law professor and gun policy expert at UCLA. "But how many times do police get these leads that people are saying things online that are intercepted as threats that don't lead to that kind of violence?"

The sheer number of shootings in the United States, however, has led to a nationwide push to rethink traditional policing when it comes to threats of mass violence. The ambitious effort would require training officers to work in multidisciplinary teams to identify troubling behavior early and monitor it over time in order to disrupt it.

"Law enforcement has to change its mindset," said Sheriff Bob Gualtieri of Pinellas County, Florida, who for six years has led a state commission investigating school violence after a gunman killed 17 people at Marjory Stoneman Douglas High School in Parkland.

"The law enforcement mindset is based on what's being told to me right now: 'Do I have something actionable?'" he said. "The right mindset in these situations needs to be whether behavior is a deviation from a person's baseline," he added, and whether that behavior "can get that person on a pathway to violence."

The FBI failed to properly investigate two tips in the months before the 2018 Parkland shooting, including one from a relative who said she feared that the gunman "was going to slip into a school and start shooting the place up." The Justice Department later agreed to pay the shooting victims' families a settlement of about $130 million.

Before the Parkland shooting, local police officers had been called to the home of the gunman, who had repeatedly made threats and exhibited disturbing behavior. Two school guidance counselors and a sheriff's deputy had recommended that he be forcibly admitted for psychiatric care, though no such committal ever took place.

Experts refer to such marked changes in behavior, including telling others of plans for violence, as "leakage" -- a drip, drip, drip of signs that someone has a perceived grievance, may not have the right coping mechanisms and may consider violent action.

"It's not necessarily prohibited behavior," Gualtieri said. "What we have to do as a best practice is get people trained, formally or informally, to recognize and understand that."

An ideal response would involve a team of police officers, mental health counselors, social workers and others to ensure that there is a support system in place to protect people from harming themselves or others. Gualtieri's office has a 72-member threat management division that meets weekly to review behavior assessments and follow up with social services as needed.

"We weren't doing this before," the sheriff said, calling it a significant but worthwhile commitment of time and resources. "It's very different to quantify averted violence," he added. "But when you're in it, you see it."

Nine states, including Florida after the Parkland shooting, now require in-school threat assessment teams to identify students at risk of committing violence, according to Everytown for Gun Safety, a leading gun control group. These teams often include members of law enforcement.

Dewey G Cornell, a forensic psychologist and education professor at the University of Virginia who helps train schools to conduct behavioral threat assessments, said that 85 per cent of US schools reported using threat assessment teams.

In his research examining more than 22,000 student threats of violence in one school year in Florida, Cornell found that very few threats were attempted or carried out; less than 1 per cent resulted in serious injury, and less than 1% of students were arrested.

"This is because most student threats are not serious and behavioral threat assessment is designed with two goals: not just identify the uncommon cases of a serious threat but also keep from overreacting to the numerous threats that are not serious," he said in an email.

"It is a complex task," he added, "but one that we found can be effective if the school has a well-trained behavioral threat assessment and management team that is given support to operate."

Crucial to effective threat assessment, including by law enforcement officials, is moving away from an approach that considers a single point in time, said J Reid Meloy, a forensic psychologist and consultant. Rather, an individual should be evaluated over time to see if his or her issues or behaviors escalate, he said.

"The metaphor I like to use is a snapshot versus a video," Meloy said. "A video is going to show you movement in time of what an individual's saying, of what's going on in the family."

Assessments should be dynamic and should change if a signal emerges that suggests an intent to be violent, he added -- such as when a weapon or additional weapon is brought into the house, or control of those weapons changes, or training to use those weapons increases.

Building threat assessment teams and training them takes considerable time and expertise, said Marc Zimmerman, co-director of the Institute for Firearm Injury Prevention and the National Center for School Safety, both based at the University of Michigan. But creating a supportive and responsive school environment is key to preventing violence, he said, and is much more effective -- and cheaper -- than hardening schools with gates, locks and metal detectors.

"I don't think there's ever been an incident that I've learned about or read about that has somebody waking up -- whether it's in a school or a workplace -- and saying, 'Oh, this is a good day to pick up a gun and shoot a bunch of people,'" he said. "There's usually bubbling grievances to the surface. The trick is to catch those things early."

And that includes changing how police think about potential shooters, too.

"The role for law enforcement has to be prevention," he said. "Because if its role is enforcing laws and dealing with a shooting, that's way too late."