PORTLAND, Maine — A man charged with killing his parents and two of their friends days after being released from prison no longer intends to use an insanity defense.

Through his lawyer, Joseph Eaton withdrew a plea of “not criminally responsible” because of mental illness but maintained a plea of not guilty in a court filing earlier this month in Sagadahoc County.

His attorney didn’t elaborate on the decision in the Dec. 8 document but noted that it means a forensic report on criminal responsibility will remain impounded. The attorney’s office was closed Wednesday and he didn’t return an email.

Law enforcement officials say Eaton confessed to the killings at a property in rural Bowdoin and to wounding three people while shooting at vehicles on busy Interstate 295 in Yarmouth.

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Killed in the shootings were Eaton’s parents, Cynthia Eaton, 62, and David Eaton, 66, along with their longtime friends, Bowdoin homeowners Robert Eger, 72, and Patti Eger, 62, officials said.

Eaton has been jailed since his arrest on April 18, the day the bodies were discovered. He was arrested near the chaotic scene along the highway.

Eaton previously told the Portland Press Herald, which first reported the change in plea, that he was not in control when he opened fire.