A Maine State Prison inmate who was serving a sentence for murdering his mother died Monday at the facility in Warren.

Joseph Fitzpatrick, commissioner of the Maine Department of Corrections, announced the death of 51-year-old Andrew Leighton, formerly of Falmouth, late Monday afternoon.

Leighton was serving a 27-year sentence for murder that began on Jan. 6, 2015.

Leighton died about 8:34 a.m. at the prison, according to Fitzpatrick. The commissioner did not offer any details about how Leighton died, and did not respond to an email seeking additional information about the circumstances that led to his death.

Fitzpatrick said the Maine Attorney General’s Office, Maine State Police and the state medical examiner were notified.

Leighton pleaded not guilty in 2014 by reason of insanity to a single count of murder in the May 3, 2013 shooting death of his mother, Shirley Leighton, 68, of Falmouth.

Leighton was accused of shooting his mother just before she and his father, Thomas Leighton, were about to have him committed for mental health treatment. Leighton lived with his parents at their home on Edgewater Road in Falmouth for about six years, according to court records.

On the day of the murder, Leighton’s father left the home to take their dog for a walk before bringing Leighton to a psychiatric facility – Spring Harbor Hospital in Westbrook. When he returned, Leighton told his father that he had shot his mother.

Leighton and his father initially struggled over a gun, a .40-caliber Baby Eagle, but his father escaped by running away. Leighton was arrested after a five-hour standoff with police.

After a series of courtroom delays, Leighton changed his plea to guilty and was sentenced to serve 27 years in prison as part of a plea agreement that was reached in January 2015.

At the hearing, Leighton’s family members continued to support him, saying publicly they believed his actions were the result of mental illness. His father said that society needs to do more to help with the treatment of people who are mentally ill.

“His mother died trying to get him help,” Thomas Leighton said in 2015. “You bring a child into this world and you don’t give up on them.”

Andrew Leighton