They were on a running track near Highlands High School when 18-year-old Neven Glen Butler allegedly jumped out and attacked Ms Arcade.

Sacramento Sheriff's Sergeant Tony Turnbull says Ms Petrus tried to defend her friend, hitting him with a "small walking stick".

"She died trying to help her friend," he said.

Butler was later arrested after a separate attack on an elderly person that afternoon.

He was being held without bail on charges of murder, felony assault and elder abuse, local authorities said.

Newshub.