No children were hurt in the late-morning shooting in the office at Louisiana Schnell Elementary School in Placerville.
Principal Sam LaCara, 50, died in the attack, police Chief George Nielson said.
Authorities said they arrested janitor John Luebbers, 44, at his home about an hour after launching a manhunt.
Investigators were trying to determine a motive for the shooting.
LaCara, who died at Marshall Medical Center, was called a dedicated leader by Bob Wells, executive director of the Association of California School Administrators.
Nielson was asked by reporters if Luebbers had been laid off. The chief said that possibility was part of the investigation, but he was uncertain about Luebbers’ employment status.
Police do not believe the janitor had a criminal history.
One student may have witnessed the shooting, Nielson said.
California Highway Patrol Lt. Chuck King said LaCara’s wife was driving on Highway 50 to the hospital after hearing about the shooting, when she was pulled over by a CHP officer for speeding. Instead of being ticketed, she was escorted to the hospital.
Police commended the school staff for quickly locking down the school and protecting the children. Students were taken to the county fairground, where they were released to their parents.
