SPRINGFIELD, Mo.—A former history professor at Missouri State University charged in the stabbing death of a colleague was found not guilty Friday by reason of insanity.

Greene County Judge David Jones announced his ruling in the case of Edward Gutting, who was charged with first-degree murder in the 2016 killing of Marc Cooper inside Cooper’s Springfield home. Cooper’s wife, Nancy, was injured but survived, the Springfield News-Leader reported.

The trial was delayed for several years in part by a series of mental evaluations. The judge’s ruling followed a six-day trial.

Marc Cooper, 66, who had retired, suffered more than 40 stab wounds. Gutting’s lawyers said the attack was the result of a schizophrenic hallucination. Gutting was diagnosed as mentally ill by several doctors after his arrest.

But prosecutors said Gutting killed Cooper in a rage fueled by alcohol and stress that stemmed from a series of work-related slights and insults. The tipping point, they said, was Gutting’s belief that Cooper meddled in Gutting’s pursuit of a tenured position.

No sentencing date was set but Jones said Gutting could be housed at a state mental health facility “for the rest of his life.”