AUBURN, Maine (AP) — A 47-year-old Maine man is using an insanity defense to charges he murdered his wife because he thought she was having an affair.

Brian Nichols, of Turner, pleaded not criminally responsible by reason of insanity at a court hearing Friday in Androscoggin County Superior Court. He had previously pleaded not guilty.

Nichols is charged with murder in the May 8, 2010, shooting death of his wife, 38-year-old Jane Tetreault.

According to court documents, one of their teenage sons told police that Nichols had bipolar disorder and had been stalking his wife after accusing her of having an affair.