Anthony Ribera, former San Francisco police chief and director of USF's International Institute of Criminal Justice Leadership, said he was surprised when he heard the officer's squad car parked in front of the driver's jeep along the roadside.
"I have never heard of that procedure. I'm at a loss; I've never heard of that," he said. "Felony stops are pretty clear that you pull up behind and leave some space behind for safety reasons."
Ribera cautioned that there could have been extenuating circumstances.
"I could speculate that perhaps they thought he would try and get away," he said.
The driver did not have any outstanding warrants.
Investigators said it was too early in the investigation to explain in detail the sequence of events but said they would review video recorded from the police dashboard camera.
Police earlier thought a second suspect may have been involved, but that person, driving a Nissan Maxima, was found, interviewed and cleared. Ribera said law enforcement officials often must combat tendencies to lower their guard when responding to seemingly innocuous calls, such as traffic stops.
"One would think more officers get shot by bank robbers than routine traffic stops, but officers are on extremely high alert when they are responding to a bank robbery where all their training comes into play," he said. "(Traffic stops) can become kind of routine, where an officer might not put up all his defense mechanisms."
The investigation into the shooting is being led by the Sheriff's office and District Attorney's Office, which is standard procedure for any officer-involved shooting that occurs in Contra Costa County.
Contact Matthias Gafni at 925-952-5026 email@example.com . Follow him atTwitter.com/mgafni . Staff writers Daniel M. Jimenez, Sean Maher, Erin Ivie, Kristin J. Bender, David DeBolt and Elisabeth Nardi contributed to this report.