A self-driving Uber car which killed a female pedestrian in Arizona was speeding when the crash occurred, police investigators revealed.
Elaine Herzberg, 49, was crossing the street on Monday when she was hit by a self-driving Uber 4x4 in Tempe, Arizona. She was taken to a local hospital where she died of her injuries.
Tempe Police said the car was travelling at around 40 mph in a 35 mph zone and preliminary investigations suggest the SUV failed to slow down before hitting Ms Herzberg.
Rafael Vasquez, a 44-year-old safety tester from Uber, was behind the wheel of the car at the time but the vehicle was in autonomous mode.
The incident is the first known pedestrian death involving a fully autonomous vehicle.
Driverless cars rely on a system of cameras and sensors along with software to detect other vehicles, pedestrians and obstacles as they navigate around cities, and the initial police findings will raise concerns over the safety of current tests being carried out by hundreds of cars across the US.
Tempe police spokesman Sergeant Ronald Elcock said impairment did not appear to be a factor Mr Vasquez or Ms Herzberg, who was walking her bicycle across the road when she was knocked down.
However Mr Vasquez has a conviction for attempted armed robbery which should have appeared in Uber's background checks and had served almost four years in an Arizona prison, according to local media.
Court records seen by The Arizona Republic newspaper show Mr Vasquez has a criminal record in Arizona under a different legal name.
Uber has previously come under fire for hiring former criminals. In November its parent company was fined $8.9 million (£6.4 million) by authorities in Colorado for hiring 60 drivers with convictions which banned them for working for rideshare companies under Colorado state law.
At the time, Uber attributed the breach to a "process area" inconsistent with the state's regulations and said all drivers must undergo a third-party background screening.
Uber has declined to comment on reports of Mr Vasquez's conviction and the company's hiring policies while the current police investigation continues.
Uber immediately suspended all testing of its self-driving fleet in cities across North America following Monday's fatal crash and said it was co-operating with the investigation.
A spokesman for the ride hailing service said: "Our hearts go out to the victim’s family. We are fully co-operating with local authorities in their investigation of this incident.”