The 44-year-old victim was found in a vehicle on the 5600 block of Orangethorpe Avenue just before 3:30 p.m. Wednesday.
Investigators have located the vehicle's owner, and they say he is not related to the victim. They are questioning him to see if he knows anything about the body.
Authorities said the victim did not live at the apartment complex, but the owner of the car does. The car was still being searched for more evidence.
Anyone with information was asked to call La Palma police at (714) 690-3370.