Unfortunate news came out Thursday after the close of a fatality in a Tesla model S. While this is not the first fatality in a tesla, it is the first that was in "autopilot' mode. After over 130 million miles of successfully navigating the world's roads, this appears to be the first that may be no fault of the driver.

Thursday the National Highway Traffic Safety Administration opened a preliminary investigation into the performance of the autopilot system featured on tesla's model s. This prompted tesla to release a statement confirming this as the first known fatality. In a blog post Thursday tesla stated:

"It is important to emphasize that the NHTSA action is simply a preliminary evaluation to determine whether the system worked according to expectations."

Thursday we also got a glimpse into what actually happened in the car accident. After all, the autopilot on the Tesla is second to none. It has the ability to detect much more than what the human eye can so how did this happen. In tesla's statement they described the incident as follows:

"What we know is that the vehicle was on a divided highway with Autopilot engaged when a tractor trailer drove across the highway perpendicular to the Model S. Neither Autopilot nor the driver noticed the white side of the tractor trailer against a brightly lit sky, so the brake was not applied."

They went on to say that the high ride height of the trailer combined with its positioning across the road and the "extremely rare circumstances" of the impact caused the Model S to pass under the trailer, with the bottom of the trailer impacting the windshield of the Model S.

So naturally this affected the performance of Tesla's (TSLA  ) stock. It traded lower by 2.5% in the after hour's on Thursday. This comes after a strong 8% rally this week, where Tesla was really starting to build up some bullish momentum.

Another name affected by this news was Mobileye (MBLY  ) which enjoyed an almost 10% gain on Thursday. The company which provides software for the autopilot system in the Tesla model S was lower by almost 3% after hours as well.

The outcome of the investigation will be interesting. For one, Tesla is very clear about the driver still maintaining active and alert control of the vehicle while it's in autopilot mode. Could a manual driver have seen and responded to the obstacle?