The legality of Musk's tweeting largely revolves around the "Reed Hastings rule" -- that is, companies can disclose important business information on social networks only if they alert investors as to where those updates will appear. If Tesla made clear that Musk might share valuable info on Twitter, the executive can likely rest easy. If it had only told them to expect news through its official accounts or its investor relations site, though, Musk could be in trouble.

There's no question that Musk had been discussing the news with the board days before, so it wasn't a completely reckless remark. However, the SEC may also want to know if the CEO already had funding lined up for a return to operating as a private company. Without it, there's a concern that Musk might have been manipulating company stock.