A sign at the entrance to Jonathan Law High School memorializes Maren Sanchez as a flag at half-staff blows in the distance on school grounds in Milford, Conn., on May 2, 2014.
Jessica Hill–AP
April 1, 2015 6:43 PM EDT

A 17-year-old Connecticut high school student accused in the fatal stabbing of his classmate nearly a year ago plans to use an insanity defense, according to recently filed court documents.

Christopher Plaskon is charged with stabbing 16-year-old Maren Sanchez in the chest and neck with a knife in a stairwell at Jonathan Law High School in Milford on the morning of their junior prom. Police have been investigating if the April 2014 attack was related to Sanchez’s refusal to be Plaskon’s prom date.

In court documents obtained by PEOPLE, Plaskon’s attorney, Edward J. Gavin, says Plaskon, at the time of the alleged offense, was “suffering from a mental disease or defect and/or extreme emotional disturbance.”

In the motion filed Monday, Gavin said he planned to introduce expert testimony about Plaskon’s mental state.

The following day, a superior court judge granted State’s attorney Kevin Lawlor’s motion to have the teen undergo a psychiatric evaluation by a mental health professional hired by the state.

“We will either verify or refute the defense’s claim,” Lawlor tells PEOPLE.

The evaluation, which will be conducted by Dr. Howard Zonana, professor of psychiatry and clinical professor of law at Yale University, will take place over the next several months.

“We are going to do our best to ensure justice is done and it will be determined based on the facts as we continue to find them,” says Lawlor.

The alleged attack took place on April 25 around 7:10 a.m. in a stairwell base by a school access door, according to a probable cause statement released by police.

A witness observed Plaskon on top of Sanchez during the attack and “actually unsuccessfully tried to pull him away from the victim,” the report states.

After the alleged assault, Plaskon, whose hands and clothes were bloody, told a school resource officer, “I did it. Just arrest me,” according to the document. Police recovered the knife in the hallway a short distance from the scene.

Sanchez, who had plans to go to the prom with her boyfriend and had posted a photo of her blue prom dress on Facebook, was friends with Plaskon, but they never dated, the New Haven Register reports.

Plaskon, who pleaded not guilty last year, is looking at 60 years in prison if convicted of Sanchez’s murder. If found not guilty by reason of insanity, he could spend 60 years at a state maximum-security psychiatric hospital or potentially released earlier if doctors decide he is no longer dangerous to himself or others, according to CBS New York.

This article originally appeared on People.com

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