The lawyer for a 17-year-old Connecticut boy charged with stabbing a classmate to death in school on their prom day says he intends to use an insanity defense.

Christopher Plaskon is charged with murdering 16-year-old Maren Sanchez in a hallway at Jonathan Law High School in Milford in April 2014, hours before the junior prom. Police have said they were looking into whether the attack was related to Sanchez's refusal to be Plaskon's prom date.

Plaskon's lawyer, Richard Meehan, released new court documents Monday saying he intends to pursue a defense of "mental disease or defect and/or extreme emotional disturbance." Meehan didn't elaborate.

Meehan has said in court that Plaskon was taking anti-psychotic and anti-anxiety medications.

Plaskon is due in Milford Superior Court for a pretrial hearing Tuesday.