The nation’s leading authority on juvenile homicide told local high school students Wednesday to stop the bullying to prevent a Columbine or Newtown school shooting.

“Most all of school shooters are bullied,” Phil Chalmers told students.

He spoke about indirect bullying, in which students do things like ignore another student, refuse to sit with the student or even create a fake social media account to destroy someone’s reputation.

“Almost all shooters come to school looking for their bullies,” he said. “Killers don’t always look dangerous.”

Chalmers showed students gathered photographs of teen killers, who all weighed less than 100 pounds.

“I’ve interviewed over 200 killers and they didn’t look like killers,” he said.

He talked to the students about a case in which a teen boy was bullied by girls and a boy who called him a “faggot.”

Chalmers said the boy brought a rifle to school and shot the teacher and then the bully. He eventually killed the whole front row and took the class hostage.

“If you want this to happen at your school, keep letting bullying happen,” he said. “When I talked to the shooter, he said to tell students that he lives in hell.”

Chalmers said girls can be some of the biggest bullies in the school.

“There has been a school shooting every week since Newtown,” he said of the aftermath of the Sandy Hook Elementary School shooting on Dec. 14, 2012.

Chalmers said in order to combat bullying and help protect schools from shooting massacres, local students and administrators must adopt a zero tolerance for bullying.

“If it takes expelling students or suspending them, do it,” he said.

Chalmers said that it’s not only the bullies who are at fault. It’s also the fault of those who laugh at the bully’s antics and those who don’t stand up for the one being bullied.

He shared signs of someone potentially getting ready to go on a shooting spree. Those things include saying they are going to shoot; being obsessed with violence and being obsessed with events like the Columbine massacre.

Chalmers encouraged students to tell someone if they saw these signs, but also tell if you are being bullied.

“Violence will land you in prison,” he said. “You will have a roommate that could be serial killer, gang member, or pedophile.”

Chalmers told students that they would be in their cells for a minimum of 23 hours per day.

He also covered tobacco use, substance abuse, before and after crack and meth photos, dangers of drunk driving, suicide, self-abuse such as cutting, teen violence, destructive entertainment such as “Grand Theft Auto,” and more.

By lunch today, every high school student in the county, and some junior high students will have heard Chalmers.

A 1:30 session is planned at Opp High School today for parents, stakeholders, and school administrators.