In an attempt to continually innovate as a company, Uber had begun testing autonomous vehicles. The self-driving car program was stopped on Monday according to the Washington Post, after a woman in Tempe, AZ was struck and killed by one of the program’s cars.

This is reportedly the first death of any testing program of self-driving cars. Tempe police said that the vehicle was in autonomous mode with a safety driver behind the wheel when the victim Elaine Herzberg was struck down “walking outside of the crosswalk.”

In a statement, Uber said, “Our hearts go out to the victim’s family. We are fully cooperating with local authorities in their investigation of this incident.”

Uber CEO Dara Khosrowshahi said in a tweet that the company was working to learn what went wrong.

“Some incredibly sad news out of Arizona,” he said. “We’re thinking of the victim’s family as we work with local law enforcement to understand what happened.”