Uber on Monday halted testing of its self-driving vehicles in North America after a woman was killed Sunday night while pushing her bicycle across a street in Tempe, Arizona.

The woman was not in a crosswalk, and there was a driver in the self-driving car used by Uber, a Volvo XC90 which was in autonomous mode, according to authorities.

Police Chief Sylvia Moir told the San Francisco Chronicle that it appears, preliminarily, that the Uber vehicle would likely not be at fault in the accident.

Moir says that after viewing a video from the car itself that the woman had emerged from the shadows onto the multi-lane road about 10:30 p.m. and that “it would have been difficult to avoid this collision in any kind of mode.”

Sunday’s crash is believed to be the first fatality in any testing program involving autonomous vehicles. The National Transportation Safety Board is investigating.

The Uber self-driving car made no attempt to brake in the 35 mile-per-hour zone, and it was apparently traveling 38 miles per hour when it hit the woman, according to the Police Department’s preliminary investigation.

Uber CEO Dara Khosrowshahi says in a tweet Monday:  “Some incredibly sad news out of Arizona. We’re thinking of the victim’s family as we work with local law enforcement to understand what happened.”