A man killed in a car crash may have had his Tesla on Autopilot while posting social media videos of himself, police have said.
The National Highway Traffic Safety Administration is investigating the crash, which happened in Fontana, 50 miles east of Los Angeles.
It is the 29th case the federal agency has investigated that involves a Tesla.
The driver Steven Michael Hendrickson, 35, died after his Tesla Model 3 hit an overturned lorry at about 2.30am on 5 May.
Another man had been trying to help the lorry driver when the Tesla hit him and left him seriously injured.
Mr Hendrickson had been a member of the Southern California branch of a Tesla club and had posted photos and videos of his car on social media.
In one video on Instagram, he was in the driver's seat without his hands on the wheel or foot on the pedal, with the comment: "Best carpool buddy possible, even takes the boring traffic for me."
California Highway Patrol said its investigation had so far found that the Tesla's partially-automated driving system - Autopilot - was engaged before the crash, although they have not determined whether it was a contributing factor.
They did not specify when the videos had been posted but did add that drivers needed to be reminded that "driving is a complex task that requires a driver's full attention".
Autopilot can keep a car in its lane and a safe distance behind the vehicles in front, but Tesla has said it is not fully autonomous and drivers must still pay attention and be ready to take over the driving at any time.
At least three people have died in previous US crashes involving Autopilot.