AUBURN — A Turner man accused of fatally shooting his wife in 2010 altered his “not guilty” plea on a murder charge Friday to claim he was not criminally responsible by reason of insanity.

Brian Nichols, 46, appeared in the Androscoggin County Courthouse library with his attorney, Donald Hornblower.

A motion he filed seeking to suppress statements he made to law enforcement authorities is scheduled for a hearing in April. A May trial is possible, a prosecutor said.

According to state law, prosecutors must prove beyond a reasonable doubt that Nichols knowingly or intentionally murdered his wife, Jane Tetreault, 38. By using an insanity defense, Hornblower must show with a preponderance of evidence that his client couldn’t appreciate the wrongfulness of his actions.

Nichols reportedly confessed to the May 7, 2010, killing, telling an Androscoggin County Sheriff’s deputy: “It’s over. I did it,” according to a police affidavit. Asked where she was, Nichols said: “She’s in bed, dead. I shot her,” according to the affidavit.

Assistant Attorney General Lisa Marchese said Friday that Nichols had at least three psychological evaluations and was found competent to stand trial.

He’s being held without bail at the Androscoggin County Jail.

According to the affidavit, Nichols told his nephew, Deputy Kevin Nichols, that he used a .30-30-caliber rifle and told him where to find it. He said Tetreault was having an affair with a man who was a client at the cleaning service where she worked and was a co-worker of hers at L.L. Bean. Police said they learned she had been afraid to go home because of Nichols’ accusations and had been sleeping at her office.

Tetreault died from a gunshot wound to the head and neck, according to the Maine Office of the Chief Medical Examiner.

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