The victim was identified as Jeffrey Cheng, 31, of Irvine, the registered owner of the vehicle.
Sheriff's officials said the car was parked in the 12000 block of Leafwood Street on Friday. Area residents alerted law enforcement after finding the vehicle with a smashed window and blood on the door.
Responding deputies found the body in the trunk of the car. Homicide detectives were investigating the incident and "working diligently to identify a suspect" in the case.
Anyone with information is urged to call the OCSD at 714-647-7000.