Attorneys for a 23-year-old Rockport man accused of killing his mother, her parents and their caretaker in September 2017 entered an insanity plea during a hearing in Middlesex County Superior Court in Lowell, Massachusetts, on Thursday.

Defense attorney Edward Wayland said that he notified the prosecution that his defense of Orion Krause will be based on lack of criminal responsibility due to mental disease or defect.

Krause’s trial had been scheduled to begin April 22. That date will now be a status hearing to see what progress the prosecution has made in its independent evaluation of Krause, the defense attorney said.

A spokeswoman for the Massachusetts Attorney General’s Office said Thursday that prosecutors don’t know when the evaluation will be complete.

Krause was indicted in March 2018 by a Middlesex County grand jury on four counts of first-degree murder. He pleaded not guilty at his arraignment in April 2018.

First-degree murder carries a mandatory sentence of life in prison.

Krause has been held in jail since he was arrested on Sept. 8, 2017, and accused of killing his 60-year-old mother, Elizabeth “Buffy” Krause of Rockport, Maine; her parents, Frank Darby Lackey III, 89, and Elizabeth Lackey, 85, both of Groton, Massachusetts; and the grandparents’ caretaker, Bertha Mae Parker, 68, also of Groton.

According to police reports, Krause confessed to police that he had killed his family with a baseball bat and said he had “freed” them.

A judge ruled in October 2017 that Krause was competent to stand trial.

Documents filed in court after his arrest detailed that his mother had called police from her home in Rockport the night before the slayings, concerned about whether he might harm himself.

She later told the dispatcher that her son was a “very mild soul,” and that there were no drugs involved.

About 20 hours later, police were called to the Lackeys’ home in Groton and found the bodies of the four victims.

An hour before their bodies were found, a professor with whom Orion Krause studied at Oberlin Conservatory in Oberlin, Ohio, called Rockport police to tell them that Krause had called to say he planned to kill his mother.

Oberlin College Professor Jamey Haddad reported that Krause told him he had “done something bad,” and had stolen some money and his mother’s car. Krause said to Haddad twice during the conversation, “I think I have to kill my mom.” The professor’s wife called police in Maine after trying to reach Orion Krause’s mother.

Police said Orion Krause had called his mother and said he was in Boston and needed a ride home. Police have not said what happened to the car he had been driving.

When his mother picked him up, she took him to her parents’ home in Groton, about 40 miles northwest of Boston.

Orion Krause – naked, covered in mud, with some blood on him – stopped at a home in his grandparents’ neighborhood to tell the resident he had killed four people.

Krause repeated his statement to police that he had killed four people and identified who they were to police, according to the police report.

Orion Krause also told a nurse during a medical evaluation after his arrest that he used heroin, police reports said.

Krause is a 2013 graduate of Camden Hills Regional High School in Rockport and graduated in May 2017 from Oberlin, where he studied music.

Friends said that Krause was a kind, musically gifted person.

Rockport police had one contact with Krause about a year before the killings, but the details of that matter have not been released. Rockport/Camden Police Chief Randy Gagne said it was not a criminal matter.