Elon Musk's August 7 tweet that he had "funding secured" to take Tesla private has become the subject of a criminal investigation by the Justice Department, Bloomberg reports, citing two anonymous sources. The involvement of the Justice Department would be significant because the Securities and Exchange Commission—which has been investigating the case for several weeks—only has the power to bring civil charges.

Tesla's share price dropped by about 6 percent in the minutes after Bloomberg reported the news.

While Musk's initial tweet claimed he had "funding secured" to buy out existing shareholders, he soon admitted he didn't actually have anything in writing. Days before the tweet, he had a meeting with Saudi Arabia's sovereign wealth fund and emerged from the meeting convinced that the Saudis would be willing to fund a deal.

"That's not what anyone in the financial markets thinks of when you say 'funding secured,'" said Stephen Diamond , an expert on securities law at Santa Clara University, in an interview with Ars last month.

A backlash from shareholders forced Musk to abandon the plan less than three weeks after his initial tweet. But that didn't put an end to possible legal complications. Tesla shareholders had already filed a number of lawsuits against Tesla, claiming that false statements by Musk had caused them to pay inflated prices for Tesla shares. And the Securities and Exchange Commission was already looking into the case.

Now, it appears that the Justice Department is looking into the case as well. In an interview with Ars Technica last month, securities law expert William Sjostrom said it wasn't common for the Securities and Exchange Commission to refer cases to the Justice Department for possible criminal charges.

Of course, it's also not common for the CEO of a publicly traded company to tweet out this kind of news without first having it vetted by securities lawyers.

Update: "Last month, following Elon’s announcement that he was considering taking the company private, Tesla received a voluntary request for documents from the DOJ and has been cooperative in responding to it," Tesla wrote in an email to Ars Technica. "We have not received a subpoena, a request for testimony, or any other formal process. We respect the DOJ’s desire to get information about this and believe that the matter should be quickly resolved as they review the information they have received."