The 75-year-old Biddeford man who is charged with killing two teenagers in an apartment at his home in December 2012 is expected to enter a new plea of not guilty by reason of insanity.

Deputy Attorney General William Stokes confirmed the news Friday but would not provide any details.

James Pak pleaded not guilty in March 2013 to two counts of murder in the deaths of Derrick Thompson, 19, and Alivia Welch, 18. Authorities say he fatally shot Thompson and Welch in the apartment that Pak rented to Thompson and his mother, Susan Johnson, 44, after a dispute over parking.

Pak has been held without bail since his arrest. He will enter his new plea during a hearing Tuesday in York County Superior Court in Alfred. His attorney, Joel Vincent, did not respond to calls for comment Friday.

Stokes said Pak has had at least one mental health evaluation in the last year. He said evaluations are common in such cases.

Melvyn Zarr, a professor at the University of Maine School of Law, said insanity pleas are rare in Maine, mostly because murder cases are rare. “You’re not going to plead insanity in a burglary case,” he said.

He said most people who read about murder cases come to the conclusion that the person charged was insane.

“But insanity is a legal definition,” he said. “And it’s difficult to demonstrate. You need experts to demonstrate that someone was insane at the time of the crime. The burden of proof is entirely on the defense.”

The shooting was reported at 17 Sokokis Road in Biddeford shortly before 7 p.m. Dec. 29, 2012. Police had been at the apartment minutes earlier to investigate a dispute between Pak and Thompson, but left after determining that the argument didn’t warrant police action.

Court documents say Pak waited for police to leave, got a gun, opened the door to the apartment and said, “I am going to shoot you. I am going to shoot you all.”

He shot Johnson first, then Thompson, then Welch, court documents say.

Johnson suffered gunshot wounds to the back and arm but survived. She called 911 after the shootings, but the two teenagers were dead by the time emergency responders arrived.

Afterward, questions were raised about how much of a threat Pak appeared to be when police responded to Thompson’s report that Pak had made death threats, and about officers’ decision to consider the confrontation a civil matter and leave just minutes before the shooting.

Police have said they determined that the dispute was a civil matter, not criminal. Thompson told the responding officers that he did not feel threatened by Pak, and no threat was made in the presence of an officer, so Pak could not be charged with criminal threatening, according to court records.

The transcripts of 911 calls made before and after the shootings were released in November, in response to a ruling by Maine’s highest court in a lawsuit filed by the Portland Press Herald.

Johnson filed a lawsuit in late January seeking at least $1 million in damages from Pak and his wife, Armit Pak, who co-owned the house at 17 Sokokis Road, including the apartment.

Johnson’s lawsuit alleges a history of disputes between Pak and Thompson and Johnson, dating back to when Thompson and Johnson first rented the apartment.

The lawsuit, and a lawsuit against the Biddeford Police Department, have been on hold pending disposition of Pak’s criminal case, said Johnson’s attorney, Daniel Lilley.

Asked to comment on Pak’s expected plea of insanity, Lilley said, “From what I know of the facts, I think that’s probably an appropriate plea.”

Insanity pleas have been used in other recent homicide cases in Maine.

Todd Gilday pleaded not guilty by reason of insanity last fall. Gilday, 44, is suspected of killing Lynn Arsenault and seriously injuring Mathew Day on Aug. 28, 2013, at Arsenault’s house at 162 Waldo Ave. in Belfast. His case is still pending.

In September, a judge found a Biddeford man not guilty by reason of insanity.

Timothy Courtois, 50, was driving 112 mph on the Maine Turnpike when he was stopped by police on July 22, 2012.

An arsenal of weapons, including an AK-47 assault rifle, and news clippings of a mass shooting in Colorado were found in his vehicle. Courtois told police that he intended to harm a former employer in New Hampshire.

Ann LeBlanc, a state psychologist, said last fall in court that Courtois’ thinking and behavior at the time of his arrest were “profoundly disturbed” and “severely disordered.”