BELFAST — The man accused of killing a well-loved Belfast woman last summer is expected to plead guilty to the crime on Monday morning, according to Maine Deputy Attorney General William Stokes.

Todd Gilday, 44, had been scheduled to go on trial in August for the slaying of Lynn Arsenault, also known as Lynn Day. Last fall, he had pleaded not guilty by reason of insanity to the charges of intentional or knowing murder, aggravated attempted murder and elevated aggravated assault.

The decision to change his plea came together on Friday, according to Waldo County Superior Court Clerk Brooke Otis.

Stokes said that Gilday is now expected to be sentenced next month. Efforts Friday to reach defense attorney Jeremy Pratt were not successful.

Police have said that Gilday was upset over a friend’s child custody case and had consumed a large amount of opiates the night of Aug. 28, 2013, when he went to Mathew Day’s Waldo Avenue home with a shotgun. He shot through the door, according to an affidavit filed in December by a Maine State Police detective, and once inside shot the 22-year-old Day in the stomach and arm, seriously injuring him.

Day told police that Arsenault, his 55-year-old mother, came out of a bedroom where she had been sleeping and may have tried to grab the gun from Gilday before he fired at her, shooting her in the chest.

Arsenault died of a single shotgun wound to the upper left arm and chest. The woman, who lived in both Garland and Belfast, was remembered by community members as a kind and compassionate person who would do anything to help others.

After the shootings, Gilday drove to Pen Bay Medical Center in Rockport, where he asked to be admitted to the psychiatric and addiction recovery unit at 1 a.m. He told the staff there he was a drug addict and had had a ” very bad night, ” according to the affidavit filed by Maine State Police Detective Dean Jackson, who said that Gilday had refused to talk to police about the case.

Day told the detective he had known Gilday for about three months and had met him through his girlfriend. Day said that he and Gilday would get drugs for each other, according to the affidavit.