Carl Ericsson of Watertown was charged in the Jan. 31 killing of retired Madison High School teacher and track coach Norman Johnson. Johnson was shot twice in the face after answering his door at his home in Madison.
Ericsson pleaded guilty but mentally ill last month to a second-degree murder charge, which carries a mandatory life sentence.
An arrest affidavit suggests the incident might have been sparked by a decades-old grudge that originated when Johnson and Ericsson were students at Madison High. Ericsson in his plea didn't specify the incident that sparked the grudge.