Michael Cedarland, 31, suffered two seizures before and after his car crashed into a Starbucks at the corner of A Street and Highway 126, according to a Ventura County Sheriff's Office accident report.
30-year old Sergio Mendez, an Iraq War veteran, was killed in the crash.
Cedarland, an off-duty L.A. County sheriff's deputy, was heading westbound on Highway 126 in his 2007 Chevy Tahoe when he veered across the eastbound lanes and jumped a curb.
He then crossed the parking lot for about 1000 feet before hitting the east wall of the store, according to the Ventura County Sheriff's Department.
Mendez was pinned between the SUV and the front door frame, authorities said.
He was taken to Ventura County Medical Center, where he died in surgery.
The two other victims -- 25-year-old Jose Iraheta and 73-year-old Thomas Michaels -- were treated and released.
Cedarland, of Pasadena, was on his way to visit a friend when the crash occurred.
According to the report, the DMV suspended Cedarland's driver's license after a May incident in which he appeared disoriented while working at the Pitchless Detention Center in Castaic, according to the sheriff's report.
His license has been suspended again.
The Ventura County Sheriff's Office will present the report to the District Attorney's Office for possible criminal charges.