PORTLAND — A Falmouth man was sentenced to 27 years in prison Monday after pleading guilty to killing his mother.

Andrew Leighton, 48, had been scheduled to take his case to trial next week, but changed his mind and accepted a plea agreement, Assistant Attorney General Leane Zainea said.

Leighton appeared in Cumberland County Unified Criminal Court on Monday morning at 10 a.m. to enter his guilty plea and receive his sentence.

Zainea said Leighton had lived with his parents for about six years at 19 Edgewater Drive while battling with severe depression and anxiety. On May 3, 2013, Leighton was taken into custody after a nearly five-hour standoff at the residence.

Police found his mother, Shirley Leighton, 68, dead from apparent gunshot wound in the living room.

Leighton’s father was out walking the dog at the time of shooting, Zainea said.

“At the time of the homicide, his mother wanted (Andrew Leighton) to go to the hospital, and he didn’t want to,” Zainea said Monday. “His mother was in the process of attempting to make a phone call, and that’s when the defendant shot her.”

Zainea said the 27-year sentence recommended by prosecutors and ultimately accepted by the court took into consideration Andrew Leighton’s acceptance of responsibility for the crime, his mental illness, the effect on the family and his show of remorse.

“He was remorseful during the investigation,” Zainea said. “He acknowledged that he had killed his mother, and during the interview with law enforcement, he demonstrated remorse.”

Attorney Robert LeBrasseur, representing Andrew Leighton, was in court Monday afternoon and was not immediately available for comment.

Leighton was originally scheduled to stand trial in late March of last year, but that date was postponed after attorneys were unable to select a jury.

Zainea said at the time that the original jury pool of about 105 people was reduced to fewer than 50 after prospective jurors completed a confidential questionnaire that included questions related to mental health. After an examination to determine the competency of each juror, there were not enough people left to select a jury, she said.

Zainea suggested that some potential jurors did not feel they could find Leighton “not criminally responsible,” which was the plea he entered at the time, because they worried he would be released from custody without supervision under that scenario.

The assistant attorney general said that had Leighton been found “not criminally responsible,” he would have been committed to a psychiatric facility, not released.

Monday’s guilty plea and prison sentence rendered that concern moot.