A teen charged with stabbing 20 fellow students and a security guard at his suburban Pittsburgh high school thought he was being controlled by the deceased Columbine shooters, a defense psychiatrist testified Monday.

A judge must decide whether to try 17-year-old Alex Hribal in juvenile or adult court for the April 2014 rampage at Franklin Regional High School in Westmoreland County. All of the stabbing victims survived.

Dr. Christine Martone, a defense psychiatrist, said Hribal believed he was being "egged on or controlled by Dylan Klebold and Eric Harris from hell."

She and a defense psychologist who have evaluated Hribal said he was psychotic and severely depressed at the time. He planned to be killed by police during the attack, they said.

However, they believe his mental health has greatly improved during treatment, and they deem him a low risk of committing a similar offense.

"I can't give you a number, but there is a very low risk here," Martone testified.

Westmoreland County District Attorney John Peck wants the teen tried in adult court, where Hribal could face a long prison term. Peck was expected to call witnesses later in the day.

Offenders in juvenile court must be released from supervision by age 21.

Spectators in the packed courtroom Monday include Hribal's parents and several people who survived the attack.

The defense experts said Hribal was fascinated with the April 1999 massacre at Columbine High School in Colorado. Klebold and Harris killed themselves after killing 13 others.