The National Transportation Safety Board (NTSB) released its preliminary report into the fatal crash involving a self-driving Uber vehicle in Tempe, Arizona, last March. Among the findings, investigators say the vehicle decided it needed to brake 1.3 seconds before striking a pedestrian, but Uber had previously disabled the Volvo’s automatic emergency braking system in order to prevent erratic driving.

The four-page report provides a detailed account of what happened that night on March 18th when an Uber test vehicle slammed into 49-year-old Elaine Herzberg, killing her. In some ways, the document is more notable for what it doesn’t say than what it does. The NTSB provides no analysis nor assigns any blame in Herzberg’s death. Much of the report has been previously reported, including the fact that Uber had disabled the Volvo XC90’s factory settings for emergency braking and other driver assist features. And there is no mention of the vehicle’s software being tuned in such a way to register Herzberg as a “false positive,” as recently reported by The Information. To the contrary, the agency said that Uber’s system appeared to be working just fine.

“All aspects of the self-driving system were operating normally at the time of the crash.”

“All aspects of the self-driving system were operating normally at the time of the crash, and there were no faults or diagnostic messages,” the NTSB says in its report.

The agency says it is continuing to work with Uber, Volvo, and the Arizona Department of Transportation as it prepares its final report, which is due in 2019. The Tempe Police Department concluded its own investigation this week, and has referred its findings to the Maricopa County attorney. A spokesperson for Uber declined to comment on the specifics of the report.

“Over the course of the last two months, we’ve worked closely with the NTSB,” the Uber spokesperson said. “As their investigation continues, we’ve initiated our own safety review of our self-driving vehicles program. We’ve also brought on former NTSB Chair Christopher Hart to advise us on our overall safety culture, and we look forward to sharing more on the changes we’ll make in the coming weeks.”

So what went wrong? The NTSB timeline of the fatal crash is as follows:

At 9:14PM, Uber safety driver Rafaela Vasquez departs the garage to run an established test run.

Immediately before the crash, she is on her second loop, traveling 43 mph north on Mill Avenue. At that moment, the car had been in autonomous mode for the preceding 19 minutes.

At 9:58PM, Herzberg begins crossing east across Mill Avenue.

The vehicle’s radar and LIDAR sensors detect an object in the road about six seconds before impact.

As their paths converge, the vehicle’s self-driving software classifies Herzberg first as an unknown object, then as a vehicle, and finally as a bicycle, with varying expectations of the future travel path.

At 1.3 seconds before impact, the vehicle’s computer decides that an emergency braking maneuver was needed. But Uber has disabled the Volvo’s factory AEB system, “to reduce potential for erratic vehicle behavior.” The system is not designed to alert the driver that braking is needed.

Vasquez intervenes “less than a second” before impact by grabbing the steering wheel. The car strikes Herzberg at a speed of 39 mph. Vasquez hits the brake less than a second after impact.

While we still don’t know exactly why Uber’s vehicle failed to brake, the NTSB cites this as the ride-hailing company’s prevailing explanation for what went wrong:

According to Uber, the developmental self-driving system relies on an attentive operator to intervene if the system fails to perform appropriately during testing. In addition, the operator is responsible for monitoring diagnostic messages that appear on an interface in the center stack of the vehicle dash and tagging events of interest for subsequent review

Vasquez was seen in a video released by the Tempe Police Department glancing down in the seconds before impact. Vasquez told investigators she had been “monitoring the self-driving system interface,” which is displayed on an iPad mounted on the vehicle’s center console. She said both her personal and business phones were in the car, but that neither was in use until after the crash.

Vasquez told investigators she had been “monitoring the self-driving system interface”

The report frames Herzberg’s actions in the moments before the crash in a fairly negative light. Investigators note she was crossing the street outside the crosswalk, wearing dark clothing, and, according to a post-crash toxicology report, had methamphetamine and marijuana in her system. The NTSB also notes that the median on Mill Avenue where Herzberg was crossing the street was not illuminated by lighting and featured signage warning pedestrians not to cross there.

But others noted that the street design where Herzberg was struck sends pedestrians a mixed message. It features an inviting, X-shaped brick-paved walking path across the median, despite being in the middle of a busy road over 360 feet from the nearest crosswalk. A homeless encampment is located a few yards beyond the median, and locals have noted that pedestrians frequently cross the street at that spot.

Immediately after the crash in March, Uber suspended its autonomous vehicle testing across North America. Subsequently, Arizona governor Doug Ducey, who had been extremely friendly toward Uber, revoked the ride-hailing company’s permission to test vehicles in the state. And yesterday, Uber said it was shuttering its test program in Arizona, laying off almost 300 safety drivers. Its self-driving program would be more scaled back and “limited” in the months to come, the company said.

Uber intends to resume its self-driving test later this year, and in some ways, today’s report was the first hurdle the company needed to overcome before getting its cars back on the road. In a recent interview with The Verge, Uber CEO Dara Khosrowshahi said he had ordered an internal review of the company’s self-driving program and would wait for those results before giving the green light to restart.

“The focus is like, just do the right thing so that I can be satisfied, the teams at [Uber’s Advanced Technologies Group] can be satisfied that hopefully nothing like this ever happens again,” he said. “You can’t guarantee anything in life.”