This is the government investigation that Tesla should be most worried about

On Monday, a report surfaced that the SEC is in the early stages of an investigation into whether Tesla failed to inform investors of some business risks prior to raising $1.5 billion in a stock sale in May.

At issue is a fatal crash in May where Autopilot, Tesla's semi-self-driving feature, was engaged on a Model S sedan.

Tesla CEO Elon Musk has forcefully disputed whether this information was "material," and the company laid out its case in a lengthy blog post.

The Florida crash is also being investigated by the National Highway Traffic Administration (NHTSA).

So that's two government agencies that Tesla has to deal with - although in fairness we should note that Tesla says it hasn't heard from the SEC, which is a clue that the regulator's inquiry isn't yet that serious.

But the real problem for Tesla is that the Florida accident is also being investigated by the National Transportation Safety Board (NTSB).

Serious business

The NTSB is serious business: these are the guys who reassemble crashed airplanes and spend years figuring out why those planes went down. These are some of the best investigators on earth. And the NTSB has sent a special team to Florida to explore exactly what happened with that Autopiloting Tesla Model S.

The NTSB is doing this because semi-autonomous driving technologies are becoming more prevalent on US roads. The government wants a high-level view on how safe this tech is, and that's where the NTSB comes in.

But Tesla is in the unfortunate position of being the company that the NTSB will be focusing on and focusing on intently.

Then again, Tesla asked for it. The automaker got out early with its Autopilot system, well before the traditional auto industry offered something similar. Musk and his team knew the risks.

The cost of those risks is being brought home: It's entirely possible that the NTSB will recommend that self-driving technologies be far more rigorously tested and regulated, placing Tesla in the position of having to disable Autopilot features or withdraw the system.

Ultimately, the SEC probe, if it's even underway, could make Tesla look bad. But so far, investors don't seem to be spooked. The stock has declined since May, but it hasn't tanked; it's now trading at $226, down from about $250 a few months back.

But a damaging NTSB report could undermine Tesla's dominant narrative: that it's the car maker of the future. That's why this is the investigation that Elon Musk should be most concerned about.