If you'll recall, the Model S in this incident collided with a tractor trailer while Autopilot was on. Since the company's semi-autonomous driving system is a fairly new technology, both the National Transportation Safety Board (NTSB) and the Securities and Exchange Commission are investigating the incident. According to NTSB's preliminary results, the car was speeding when it crashed into the bigger vehicle.
It's worth noting that the automaker considers its braking system a separate entity from Autopilot, which is in charge of steering and changing lanes. Tesla has always denied that the accident was caused by Autopilot, though it ended up breaking things off with the company that made its image recognition hardware. A statement Tesla released in June only said that "Neither [the feature] nor the driver noticed the white side of the tractor trailer against a brightly lit sky, so the brake was not applied."
This article by Mariella Moon originally ran on Engadget, the definitive guide to this connected life