Fontana police were called to the 11200 block of Poplar Avenue around 6:30 a.m. regarding a shooting in the parking lot of a logistics company.
Responding officers found two men with apparent gunshot wounds at the scene.
One man was transported to a local hospital, where he was pronounced dead. The second man was pronounced dead at the scene.
Detectives believe the incident was a murder-suicide.
It's not known if the two men worked at the business. No workers inside the facility were threatened or injured, authorities said.
The investigation was ongoing.