There were also reports that the driver had been watching a movie at the time of the accident, as well as questions about whether he had been operating the Autopilot feature consistent with Tesla's instructions.
NHTSA is sending a five-person team to Florida later this week to investigate that crash, said Christopher O'Neil, a spokesman for the agency, which makes recommendations to regulators and companies about transportation-related safety issues.
Tesla's shares fell 1% in after-hours trading after the report about the perceived SEC investigation.
Tesla spokeswoman Alexis Georgeson said the company was aware of the Montana accident and is looking into it. The SEC declined to comment to CNBC. Longtime Tesla followers will recognize this as the plan Musk formally introduced in August of 2006, which described Musk's eventual goal of releasing the Model 3, the company's affordable EV now slated for a late 2017 release. Regulatory bodies could require more restrictions on Tesla's autopilot, but the challenges would be something the company would be able to respond to-using more sensors to require drivers to show active engagement while using the autopilot features, for instance. Brown, who died at the scene, was an avid fan of Tesla who had posted dozens of videos of himself using the vehicle in its autopilot mode. According to Tesla, the extent of the damage to the vehicle limited the the ability to remotely recover data and that "it was not until May 18th that a Tesla investigator was able to go to Florida to inspect the auto and the crash site and pull the complete vehicle logs from the car" to determine whether the Autopilot system was active. Tesla did unveil its Powerwall home battery technology previous year.
Joshua Brown, 40, of Canton, Ohio, died May 7 in Williston, Fla., when his Tesla Model S car's Autopilot system failed to detect a tractor-trailer turning in front of the luxury electric vehicle.
Elon Musk SpaceX is the third company founded by Mr. Musk.
And he's also said that Tesla could be worth more than $700 billion in less than 10 years.
Tesla CEO Elon Musk called the fatal accident "not material" to shareholders, defending the automaker's decision not to publicize the fatal accident until June 30th.