When Norman Johnson answered his door January 31st, little did he know that the man on the other side of the door had a gun. The 73-year old gunman was there to settle a grudge that dated back to the time the two were in high school together.

Johnson was shot in the face and died that night. The suspect, Carl Ericsson, was arrested a few days later.

On Tuesday, Ericsson pleaded guilty but mentally ill to a charge of second-degree murder. The plea was entered in a courtroom in Madison, South Dakota.

Johnson and Ericsson were students at Madison High School back in the day. Johnson ended up being a teacher and track coach at the school until he retired.

A few weeks after the shooting, Ericsson pleaded not guilty to a charge of first-degree murder. He requested a jury trial at the time. However, his defense attorney Scott Bratland and Lake County State’s Attorney Kenney Meyer announced on May 1 that a deal had been reached on the lesser charge.

Ericsson faces a mandatory sentence of life in prison.