Federal investigators from the National Highway Traffic Safety Administration have demanded automaker Tesla hand over details about a fatal May crash that occurred while a car was in autopilot mode.

NHTSA, in a letter sent Friday to the car company, asked for all documentation related to the crash that killed Joshua David Brown, 40, of Canton, Ohio, in Williston, Fla., on May 7. The agency also requested information regarding the programming and manufacture of Tesla's Automatic Emergency Braking system, a product designed to assist autopilot and prevent frontal collisions.

Tesla's responses are due back to the federal authorities in part by July 29 and in part by Aug. 26. The company could face $21,000 in fines per day if it is late.

"This is a huge moment," Kelley Blue Book analyst Michael Harley said. "Up until now, the whole autonomous thing has been this new technology consumers have been buying into. The reality is that any new technology poses dangers, including injuries and death."

Brown was driving his black 2015 Model S Tesla in autopilot mode on U.S. Route 27 in Williston and hit the side of a tractor-trailer that was crossing the road to make a turn.

"Neither autopilot nor the driver noticed the white side of the tractor-trailer against a brightly lit sky, so the brake was not applied," Tesla said in a blog post this month titled "A Tragic Loss." A Tesla spokesman declined to comment further Tuesday.

The Model S passed under the trailer, crushing the top of the car and the windshield.

"Had the Model S impacted the front or rear of the trailer, even at high speed, its advanced crash safety system would likely have prevented serious injury as it has in numerous other similar incidents," Tesla said in the blog post.

"NHTSA submitted its Information Request to Tesla as a standard step in its Preliminary Evaluation of the design and performance of Tesla’s automated driving systems in use at the time of the May 7 crash in Florida," the agency said in a statement. "NHTSA has not made any determination about the presence or absence of a defect in the subject vehicles."

The crash marked the first fatality in more than 130 million autopilot miles driven, according to Tesla.

In the letter, NHTSA also asks Tesla for its internal investigation of the crash and all other customer complaints about the semi-autonomous system.

Autopilot mode uses cameras and sensors to detect traffic or other obstacles around a vehicle and allows the car to maintain speed and stay in its lane. The car periodically asks drivers to place their hands on the steering wheel to confirm that they remain in control of the vehicle even as it steers itself.

In dire circumstances, the car will also immediately return complete control to the driver.

Brown had a YouTube channel on which he posted videos of himself driving his Model S, nicknamed "Tessy," in different road conditions. In April, he posted a video of the car in autopilot mode that successfully swerved to avoid an oncoming boom lift truck that moved into his lane.

The investigation, though a routine procedure for NHTSA, casts a pall over the autonomous car movement as automakers await regulators' word on the safety of this technology. Other car manufacturers and even technology giants also have billions of dollars invested in autonomous driving systems.

BMW, for example, last week announced a joint venture with multinational technology firms Mobileye and Intel to launch a self-driving car. Google has billions of dollars invested in its own autonomous vehicles.

"Everyone is sitting here waiting to see how Tesla and Elon will respond to this," Harley said, referring to Elon Musk, the car company's owner. "This has to be the biggest story in the entire auto industry. It's a big deal, a very big deal, and it’s very serious."