MILFORD, Conn. — A 16-year-old boy charged in the fatal stabbing of a high school student on the day of the prom is showing signs of an active psychosis, his attorney said Friday.

Christopher Plaskon, who made his first court appearance Friday, has been charged with murder in the slaying of Maren Sanchez, a friend who was stabbed to death last week in a hallway at Jonathan Law High School in Milford.

Plaskon showed no emotion during the brief hearing. He wore handcuffs and leg shackles and no shoes as he stood next to his attorneys and his uncle Paul Healy, who was appointed his guardian.

Plaskon was ordered transferred to the state’s Manson Youth Institution in Cheshire, where lawyer Richard Meehan asked that he be placed at a hospital under a suicide watch. He will not enter a plea until after a probable cause hearing, which is scheduled for June 4.

Meehan did not provide details of Plaskon’s condition, but he did say the boy understands he’s charged with murder and that Meehan is his attorney.

The attack occurred last Friday, hours before the school’s junior prom, and police have been investigating whether it was related to Sanchez’s refusal to be Plaskon’s prom date.

Plaskon is being held on $3 million bond.

Meehan said Plaskon’s parents wanted to attend the hearing, but he recommended against it because he believed it would be too difficult. He said they are in seclusion.

“All their hearts are broken,” Meehan said, referring to Plaskon’s family. “I think the word numb is probably the best word I could use to describe what these people are going through.”

Plaskon was arraigned Tuesday at a medical facility, where his attorneys have said he has been undergoing psychiatric evaluation.

State’s Attorney Kevin Lawlor decided Plaskon will be prosecuted as an adult, and not in juvenile court.

A witness saw Plaskon on top of the 16-year-old victim during the attack, and tried unsuccessfully to pull him away, and another saw him discard a bloody knife, according to a police affidavit. Plaskon, his clothes bloody, was taken to the principal’s office, where an officer arrived and asked what happened. “I did it. Just arrest me,” Plaskon replied, according to the officer.