CAMBRIDGE, Mass. (AP) – A 16-year-old Princeton boy charged with fatally stabbing a high school classmate “terrorized other students” with talk of weapons, and searched for a random victim on the morning of the slaying, a prosecutor said Tuesday.

John Odgren followed James Alenson, 15, into a bathroom at Lincoln-Sudbury Regional High School on Jan. 19 after no one entered a separate bathroom Odgren had staked out, Assistant District Attorney Daniel Bennett said.

“The defendant, John Odgren, did not know James Alenson, had not been teased by James Alenson, had not been shunned by James Alenson, did not even know his name,” Bennett said.

Odgren slashed Alenson’s throat before stabbing him through the heart and in the abdomen, Bennett said.

A third student was in a bathroom stall and heard Alenson say, “What are you doing, you are hurting me,” Bennett said.

As Alenson stumbled into the hallway, the third student emerged from the stall and Odgren said, “Don’t worry, I’m not going to hurt you,” Bennett said.

Odgren allegedly kneeled beside the dying Alenson and checked his pulse.

“I did it. I just snapped. I don’t know why,” Odgren allegedly told a teacher who ran to the scene, Bennett said.

Odgren, who was indicted last week, appeared in Middlesex Superior Court and pleaded not guilty to first-degree murder.

Odgren has been in custody since the day of the killing. His lawyer, Jonathan Shapiro, asked Judge Isaac Borenstein to release Odgren to a secured ward of the Westborough State Hospital, where he could get better psychiatric care.

Borenstein agreed to send Odgren to Westborough for a 20-day evaluation, but ordered that Odgren remain in custody without bail.

Shapiro said his client is under suicide watch at a juvenile jail in Plymouth, and that his mental condition is deteriorating.

After the hearing, Shapiro said Bennett’s version of events is “completely outrageous.”

“Most of what he said today is untrue, will be shown to be untrue, and a lot of it is a figment of someone’s imagination,” Shapiro said.

Odgren suffers from Asperger’s Syndrome, a form of autism, and hyperactivity disorder. He had been in a special needs program housed at the high school, and has been taking medication for many years. People with Asperger’s generally have a normal to genius level intelligence, but may fixate on certain things and be unable to read social cues or sense the feelings of people around them.

Bennett told the court that Odgren had a history of threatening behavior at the school, nestled on a wooded campus 17 miles west of Boston.

“At different times through his knowledge of forensics, weapons, and his knowledge of other horror stories, he terrorized other students,” Bennett said.

Odgren once chased a student while holding a shard of glass and told other students that he knew how to commit the perfect murder, Bennett said.

Bennett said Odgren played a violent video game the morning of the killing, and in prior days said goodbye to online friends.

Sudbury Police Chief Peter Fadgen said on Saturday that Odgren brought a fake gun and small folding knife to school on separate occasions before the stabbing. He said a psychologist working with Odgren confiscated the weapons, but gave them back at the end of the school day.

Odgren once took a forensics class at a community college near his home.

At Westborough, Odgren will be treated by a team of psychologists that includes the one who confiscated the weapons from him at school, Shapiro said.

John Ritchie, principal of the high school, did not immediately return a phone message left after school hours by The Associated Press.