A Connecticut teenager has pleaded no contest to murder and faces up to 25 years in prison for stabbing a classmate to death at their high school on junior prom day in 2014.

Eighteen-year-old Christopher Plaskon accepted a plea bargain Monday in Milford Superior Court. Sentencing is set for June 6.

Plaskon was charged with killing 16-year-old Maren Sanchez at Jonathan Law High School in Milford on April 25, 2014. His family and friends said he had been upset Sanchez turned down his prom invitation.

Plaskon was held at a psychiatric hospital after the attack. His attorneys said he showed signs of psychosis and they were considering an insanity defense.

Sanchez was a member of the National Honor Society and active in drama and other school activities.