Uber has determined that the incident between a pedestrian and an Uber vehicle undergoing autonomous driving trials which led to the death of Elaine Herzberg was due to a bug in its software, according to The Information.

Apparently, the vehicle’s sensors detected the pedestrian, but the software determined that it did not need to react immediately as part of its protocol to ignore ‘false positives’, such as a plastic bag floating in its path. In the incident involving Herzberg, Uber disabled the standard collision avoidance system on the Volvo XC90 test vehicle, likely to avoid systems conflicts with its own setup it was testing at the time.

Uber and the National Transportation Safety Board have ongoing investigations into the incident to determine whether or not the software is at fault, but sources who were briefed on the initial findings told The Information that the software could be to blame.

“We have initiated a top-to-bottom safety review of our self-driving vehicles programme, and we have brought on former NTSB Chair Christopher Hart to advise us on our overall safety culture. Our review is looking at everything from the safety of our system to our training processes for vehicle operators, and we hope to have more to say soon,” an Uber spokesperson said in a statement.

Uber halted its testing of autonomous vehicles since the fatality, and the Arizona state governor suspended Uber’s ability to test and operate autonomous vehicles on Arizona’s public roads. Uber’s operators of self-drving vehicles were required to take back control of the car an average of once every mile (1.6 km), Recode reported, and that it was also struggling to meet its goal of driving 13 miles (20.8 km) on average without having the driver intervene, the New York Times said.

Last month, Uber said that it believes the prospects for autonomous vehicles are still positive despite the high-profile incident, and that they will be safer at maturity and in the long-term, key to eliminating individual car ownership. It had previously constructed a 42-acre ‘fake city’ with roadways, complicated intersections, fake cars and unpredictable pedestrians as an environment for testing its autonomous vehicles.