A U.S. National Transport Safety Bureau investigation into a fatal accident involving an Uber Technologies Inc. in March has preliminarily confirmed that not only was Uber’s software to blame but the company had also disabled the emergency braking feature in the vehicle.

The crash in March involved an Uber test vehicle in autonomous mode hitting and killing a pedestrian at night in Tempe, Arizona. The accident was initially believed to be a case of the victim having walked out into the path of the self-driving vehicle, giving the technology no time to react.

A subsequent internal investigation by Uber found that the technology was behind the fatal crash, in that the autonomous vehicle software had been set in a way that caused it to ignore the pedestrian. In particular, that investigation found that the technology deployed on the self-driving car, including its LiDAR, radar and cameras, all detected the pedestrian despite the fact that she was crossing the road in the dark.

The NTSB confirmed the results of Uber’s investigation in a preliminary report issued Thursday, saying the vehicles radar systems observed the pedestrian six seconds before impact, but “the self-driving system software classified the pedestrian as an unknown object, as a vehicle and then as a bicycle with varying expectations of future travel path.”

However, though the software was found at fault, the report also found that Uber had disabled the emergency braking system, a standard feature in the Volvo XC90 test vehicle, while the vehicle was under computer control to reduce the potential for erratic vehicle behavior. Worse still, the software itself detected the need to apply emergency braking, but because it was disabled, it couldn’t do so.

The implication of the finding is that although there were faults in the software, ultimately it was Uber’s intentional decision to disable emergency braking that led to the fatality rather than the accident itself. Had the emergency braking been applied, the speed of the vehicle at impact would have been significantly less, reducing the chances of the pedestrian being killed.

Since the NTSB report is only preliminary, it doesn’t conclude with any recommendations. But as Reuters reported, its publication has given fuel to Congressional opponents who have stalled a bill created to speed the deployment of self-driving cars on U.S. roads.

Uber has yet to respond to the report but announced earlier this month that it had hired Christopher Hart, the former chairman of the NTSB, to advise it on safety.

Image: Uber