Police say the principal at Louisiana Schnell Elementary School, Sam LaCara, got into an argument with the school janitor just before the shooting, which happened about 10:30 a.m. Wednesday.
It is unclear what the argument was about. Police say the gunman may have confronted the principal over some perceived grievance. Police are also looking into reports that the janitor may have been laid off Wednesday.
The gunshots sent the campus into lockdown for the safety of the students and to protect the crime scene.
No children were hurt.
LaCara, 50, was immediately rushed to Marshall Medical Center, where he died at 11:15 a.m. from a gunshot wound to the torso.
Students were bused to nearby fairgrounds where parents could later pick up their children.
Police identified the gun man as 43-year-old John Luebbers and arrested him at his home. The police chief believes Luebbers did not have a criminal record.
One parent told the Sacramento Bee newspaper that parents have been trying to get rid of the janitor for a long time because he was mean to kids.
Another parent said her daughter hugged the janitor and he bought Girl Scout cookies from her.
The shooting in this normally quiet school in town has people on edge, especially the students.
"We believe that one student may have witnessed this shooting," said Placerville Police Chief George Nielsen. "I'll also add that we immediately had three chaplains respond to work with family, students obviously and emergency responders."
"Our kids are going to be traumatized for sure," said parent Michelle Vien. "I don't really know how to tell them that their janitor shot and killed their principal. I have no idea how to tell them that."
Luebbers had not been formally charged Wednesday evening.
Principal LaCara is remembered as a married father of three who had a great sense of humor and a love of sports.