MILFORD, Conn. (AP) - A Connecticut teenager has been sentenced to 25 years in prison for fatally stabbing a classmate after she turned down his invitation to prom.

A judge handed down the sentence to 19-year-old Christopher Plaskon on Monday in Milford Superior Court.

Plaskon pleaded no contest to murder in March in the killing of 16-year-old Maren Sanchez inside Jonathan Law High School in Milford on the day of the junior prom in April 2014.

Plaskon's family and friends say he was upset with Sanchez for rejecting his invitation.

But his lawyer said the stabbing wasn't related to prom. His attorneys said he showed signs of psychosis and they considered an insanity defense.

Sanchez's parents are suing Plaskon, his parents and the Milford school system.