ST. LOUIS — One of the two armed seniors at Columbine High School in Colorado who murdered 12 students and a teacher had shown signs that he was a fledgling psychopath with antisocial traits — someone capable of becoming a cold-blooded killer.

The lone gunman who murdered 32 people in the 2007 Virginia Tech massacre had been diagnosed with a severe anxiety disorder.

Adam Lanza, the 20-year-old shooter at Sandy Hook Elementary School in Newtown, Conn., was known to be socially awkward and had difficulty coping with daily life.

In recent decades, mental health experts and law enforcement officials have attempted to use “threat assessment” principles to help identify people who may be a danger to the community.

But there is no simple formula to determine who might be the next shooter, experts say, and such attempts at profiling run the risk of misidentifying individuals who may only be suffering from depression or a behavioral disorder.

People who constantly spew threats of violence may never follow through on their words, and someone who seems sociable and mild-mannered can turn out to be the next mass murderer.

“We don’t know everything that goes on in the brain and what sets these things off,” said Dr. Annemarie Loth, a pediatric psychiatrist and professor at St. Louis University. “Behavior is still a choice. Our environment plays a role. Their biology plays a role.”

However, she and other mental health experts stressed that psychiatric care and medication can go a long way toward treating a person’s illness.

In 2002, the U.S. Secret Service found in its investigation of 37 school shootings that while most all of these massacres are pre-planned, there is no accurate or useful “profile” of students who engage in targeted school violence. Not much has changed to alter that conclusion, except that the list of horrific massacres has grown.

The Secret Service found that most of the shooters — whose ages ranged from 11 to 21 — came from two-parent families, socialized with mainstream students, had no history of violent or criminal behavior, and had never or rarely been in trouble at school.

Only a third of the attackers had received a mental health evaluation, but most had exhibited a history of suicide attempts or thoughts. Many of the attackers felt bullied, persecuted or injured by others prior to the attack.

“It’s very hard to predict, and if you cast too big a net, then what do you do?” said John Eiler, president of the St. Louis Regional Psychiatric Stabilization Center, which has short-term beds for people in crisis. “What would we have done in Aurora (the site of a mass shooting in July inside a Colorado movie theater) or Connecticut? Would we have had enough information beforehand to say: This person needs to be institutionalized? Probably not.”

Following the Columbine massacre in 1999, the FBI created a “school shooter” assessment that it said would help teachers spot potential killers among students and head off similar attacks.

The study listed various traits of concern, from comments and writings that show an obsession with violence to attitudes of intolerance and superiority as well as the development of negative role models such as Adolf Hitler or Satan.

But the FBI conceded that “there is no magic number of traits or constellation of traits which will determine what students may present a problem.”

Following the Virginia Tech massacre, college administrators across the country have focused on identifying potentially dangerous students.

Many colleges have created “threat assessment teams” of administrators, counselors and campus police officers to track disruptive students and those with mental health issues. The teams monitor and interview students of concern, attempt to gauge the credibility of specific threats, and to intervene in a timely manner.

At the University of Missouri in Columbia, the “at-risk behaviors team” meets bimonthly in part to discuss individual students who are deemed to be a potential danger to themselves or others. Mizzou conducts screenings for depression and stress — and helps connect students with counselors. Campus police conduct “well-being checks” on students who are not attending class.

“It’s hard to measure what you prevent, but we feel like we have done pretty well,” said Cathy Scroggs, vice chancellor for student affairs.

High schools and middle schools, too, are also attempting to recognize the warning signs of potential violence and to manage overly aggressive students.

Dr. Eric Rossen, director of professional development and standards at the National Association of School Psychologists in Bethesda, Md., said that although threat assessment is not an exact means of predicting future behavior, it has “helped at least to some degree to identify students who are at heightened risk” and provides appropriate interventions.

Rossen and others caution that having a developmental disability or psychiatric disorder does not usually predispose a person to acts of planned violence.

He said that providing a full range of mental health services, starting with a supportive classroom and campus environment but also including emotional and behavioral screening and psychological counseling, is “probably our best approach to preventing violence in the schools.”

Dr. Thurma DeLoach, executive director of special programs for the Kirkwood R-7 School District, said the school system — which includes preschool through 12th grade — employs various screening techniques to identify students in need of extra counseling services.

“All of my colleagues have this on our radar,” DeLoach said. “It’s not specifically ‘threat’ that we’re looking for, but a student who is somewhat off-track or clearly off-track, someone with social and emotional behavioral issues that are not typical. We’re looking for the kids who would be the outliers.”

She said that “education support counselors” work closely with troubled students and their families as well as school administrators and any outside mental health professionals that a student’s family has obtained.

School officials can help identify troubled and potentially dangerous youngsters, but many schools have limited resources for counseling.

“When a school calls with a kid in crisis, that’s considered a high priority case,” said Dr. Bart Andrews, director of clinical resources for the Behavioral Health Response crisis intervention center in St. Louis. “That typically results in our mobile outreach team being sent out.”

The mobile team evaluates the student and tries to get the child’s parents involved. Counselors determine whether the student’s safety and the safety of others can be ensured, and make any arrangements for hospitalization if needed. If the youngster needs counseling, they attempt to set up a next day or urgent appointment.

Local mental health experts said that concerns about disturbed and potentially violent youngsters extends to even the pre-kindergarten level. Some young children are extremely anxious and withdrawn, others are highly aggressive.

Sally Brown, an early childhood special education teacher who has worked in both St. Louis City and St. Louis County, said that preschools are increasingly experiencing children as young as four and five years old who occasionally exhibit behaviors that are surprisingly violent.

These children occasionally lash out at adults and children with an unpredictable rage that goes way beyond typical childhood tantrums — turning over heavy cabinets, using scissors as weapons and choking.

“The reality is that we’re ill-equipped to do much of anything,” Brown said. “We don’t have the training or the resources … because they are so young.”

Most often, the police are called upon to intervene with adults and teenagers in crisis. When necessary, police have the authority to hold someone for 96 hours in “protective custody” for psychiatric evaluation. But most hospital admissions in psychiatric wards are voluntary.

“We don’t want to force them and put them in handcuffs in an ambulance,” said St. Louis County Police Sgt. Barry Armfield, the crisis intervention team coordinator for the St. Louis area. “We would much rather have them go voluntarily.”

He said that police beat officers receive special training on mental health issues and use investigative techniques to assess a person’s potential dangerousness.

In St. Louis city and county, officers write 250 to 300 reports a month regarding people in emotional crises. Eighty-nine percent of these subjects are taken to a hospital emergency room for a psychiatric evaluation, most of them voluntarily.

“The police are doing their job, but there is just not money out there for an individual who is sick to receive the proper treatment,” Armfield said. “Mental health needs to be funded so that after we identify individuals who are a possible threat to the community, they can receive the treatment they need.”