The three-vehicle collision occurred shortly before 5 a.m. near the intersection of Bullis Road and Compton Boulevard, the sheriff's department said. A damaged LASD vehicle, another SUV and a mangled car were seen at the crash site.
"I heard boom, boom, boom - and that was it...I didn't hear a siren at all," resident Jerry Guerra said.
The dispatcher was with the deputy as part of a training exercise, authorities said. The two were on patrol and were not responding to a call when the crash happened.
While the sheriff's personnel and the civilian were hospitalized with non-life-threatening injuries, a fourth person was treated at the scene for minor injuries.
Nearby residents a business owners said the stretch of road is dangerous when it comes to traffic crashes.
"It's a pretty bad corner. There's always an accident out here. At least once a week here there's an accident. We don't know if it's the light, or they're misjudging the light, or what's going on," Victor Robbins said.
The barber shop owner said the crash shattered the front door of his barber shop. He said he wouldn't let it affect his business this time and rerouted his customers around the back.
But he added that he hopes something can be done so that the next accident isn't deadly.
The intersection was closed for more than five hours as investigators from the department's Traffic Services Detail collected evidence and examined the wrecked vehicles.
The cause of the incident was unknown.