A man who confessed to killing his parents and their two friends before going on a random shooting spree on a Maine interstate last year has pleaded guilty to more than a dozen charges, including murder, and was sentenced to life in prison on Monday.

Joseph Eaton, 35, pleaded guilty on Monday to intentional or knowing murder, aggravated attempted murde,r and additional charges of theft and cruelty to animals in Sagadahoc County Superior Court. Eaton received the maximum penalty for each charge, including life sentences for each of the murders.

Authorities said Eaton had confessed to killing his parents and two of their friends in a Portland-area home in April 2023. He then fled to Interstate 295 in Yarmouth — a town about 12 miles northeast of Portland — and fired at passing vehicles, injuring three members of an area family.

Although authorities have not released any motives on the shootings, Eaton and his attorney agreed with some family members and friends of victims who testified that the 35-year-old should be punished to the fullest extent of the law, WGME-TV reported.

"I wake up every day regretting what I did," Eaton said in court Monday, according to WGME-TV. "A life sentence is what I deserve and honestly, I think I deserve worse. All I can say is, I’m sorry."

Eaton initially pleaded not guilty and entered an insanity plea in July 2023 but withdrew the plea last December, according to court documents. Eaton told the Portland Press Herald in interviews last year that he was not in control of his actions during the shootings, and had a history of childhood sexual abuse, mental health issues, and drug use.

He described feeling a "psychotic break" before the shootings occurred, according to the newspaper.

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4 killed, 3 injured in violent rampage last year

Authorities arrested Eaton on April 18, 2023, within hours after the bodies of his parents and their two friends were discovered in a home in Bowdoin, a small town about 36 miles northeast of Portland.

Police said Eaton had confessed to fatally shooting his parents, Cynthia and David Eaton, and their friends, Patricia Eger and her husband, Robert Eger. He also admitted to killing the Egers' dog, which resulted in the animal cruelty charge against Eaton, according to court documents.

An arrest affidavit for Eaton revealed that Patricia Eger's sister had discovered the victims after she saw blood on the front steps of the residence. Police said the Egers owned the home and the Eatons were staying with them at the time of the incident.

"Lisa opened the door and yelled but no one answered. Lisa said she entered the home and could see broken glass and blood on the floor. She observed a body in the area of the kitchen covered by a towel," the affidavit stated.

Investigators who arrived at the scene found an unsigned note that said "someone had been molested and that there was nothing done about it," according to the affidavit. The note also mentioned "someone being freed of pain and that the writer of the note wanted a new life."

Authorities believe the victims were killed on April 17, 2023, and after their bodies were discovered the next day, Eaton fled in his parents' rental car to a nearby interstate in Yarmouth. Eaton said he believed that he was being chased by police and fired at passing vehicles on the highway, injuring three members of a family.

Eaton faced two separate indictments because the incidents occurred in different counties, according to court documents.

Joseph Eaton had a criminal history

Eaton had been released from a Maine prison just days before the shootings, according to court records. He had served about a two-year sentence for assault, USA TODAY previously reported.

Under Maine law, Eaton was prohibited from possessing firearms because of his prior convictions. Court documents showed that Eaton was charged with stealing firearms from his mother and Robert Eger.

The Bangor Daily News reported last year that Eaton's parents had asked authorities in 2017 to release him to their custody to serve out his probation for a Maine crime. At the time, the Eatons were living in Florida.

But in 2018, Eaton was arrested by Florida authorities following a violent incident at a relative’s home, according to the newspaper. He then served three years in a Florida prison before he was returned to Maine.

Contributing: Trevor Hughes, USA TODAY