The Alameda County Sheriff's Office said later it was one of their young employees who was "murdered" while driving home from work.
Officials did not release his age or name, but said he was a recruit who was graduating in February.
They say he was driving home from the academy, in his personal car and not in uniform, when he was shot.
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There is no word on whether he was targeted or if this was a random shooting.
Alameda County Sheriff's Office did say, "This appears to be another senseless act of gun violence on a Bay Area freeway."
The CHP says it started when they responded to a report of a crash at the I-580 and I-80 transition around 4:30 p.m.
When officers arrived they found the car up against the guardrail with moderate damage and the driver suffering from a gunshot wound. He was taken to the hospital where he later died as a result of his injuries.
"An unknown assailant fired a gun into the personal vehicle of our recruit, killing him and causing his vehicle to crash," the Sheriff's Office said.
Alameda County Sheriff's Office said on Twitter they are "heartbroken and disturbed by this senseless act of gun violence."
The CHP is investigating the shooting and asking anyone with information about the incident to call the CHP Investigation Tip line at (707) 917-4491.
CHP Oakland will be the lead investigating agency.
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Stay with ABC7 News for the latest details on this developing story.