The U.S. Justice Department has opened a criminal investigation of Tesla, examining public statements made by the company and its CEO Elon Musk, two news organizations reported on Tuesday.

Bloomberg News and the Financial Times reported, based on anonymous sources, that U.S. prosecutors began a fraud investigation after Musk tweeted last month that he was considering taking Tesla private and that the funding for such a transaction was “secured.”

The electric automaker had already received a subpoena regarding the matter from the U.S. Securities and Exchange Commission, the federal enforcer responsible for civil securities fraud.

Tesla said that it did receive a request for documents from the DOJ but it did not respond to a question about whether it agreed with the description of the inquiry as a criminal investigation.

“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,” a Tesla spokesperson said in an email. “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.”

The U.S. Attorney’s Office in San Francisco would not confirm or deny the existence of a criminal probe.

On Aug. 7, Musk tweeted that he had a plan to take Tesla private, sending shares up 11 percent on the day. The company went public in June 2010 and has enjoyed a strong run in recent years as optimism for the future of electric vehicles grew.

Am considering taking Tesla private at $420. Funding secured. — Elon Musk (@elonmusk) August 7, 2018

After weeks of speculation about the plan and whether Musk had financing in place, Musk reversed himself on Aug. 24 and said that most shareholders believed Tesla was better off as a publicly traded company.

Publicly traded companies and their executives are bound by strict laws regarding the dissemination of sensitive financial information.

A federal rule prohibits them from announcing plans to buy or sell securities if they don’t intend to follow-through, don’t have the means to complete the deal or are trying to manipulate the stock price. Another rule bars them from making “any untrue statement of a material fact.”

Shares in Tesla fell on Tuesday after news of the criminal investigation, down 3.7 percent in mid-afternoon trading.