Tech billionaire Elon Musk is being investigated by the FBI in connection with his $44 billion takeover of Twitter. The information came from a court filing made public on Thursday about the latest in the billionaire's ongoing legal battle with the social network.

While the filing stated that he was being investigated, it did not specify the nature of the investigation. "This game of 'hide the ball' must end," the company said in the court filing.

Twitter, which sued the SpaceX chief in July to force him to close the deal, said Musk's lawyers claimed "investigative privilege" when refusing to turn over documents it requested.

It also stated that it had requested months ago that Musk's attorneys produce their communications with federal authorities, but that they had not done so.

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Musk's attorneys provided a "privilege log" in late September, identifying documents to be withheld. The log referred to drafts of an email sent to the US Securities and Exchange Commission (SEC) on May 13 - the American regulator in charge of enforcing market manipulation laws.

It also referred to a slide presentation given to the Federal Trade Commission, whose primary mission is to promote antitrust law and consumer protection.

The court request was made on the same day that the court granted a stay of proceedings to allow Twitter and Musk to complete the takeover deal.

Questions over the deal

The SEC has repeatedly questioned Musk's comments about the Twitter acquisition. It first questioned him in April about whether his 9% Twitter stake was disclosed late and why it indicated that he intended to be a passive shareholder. Musk later amended his disclosure to reflect that he was an active investor.

The SEC asked Musk in a letter in June whether he should have amended his public filing to reflect his intention to suspend or abandon the deal.

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An attorney for Musk, Alex Spiro, told Reuters that Twitter's court filing was a "misdirection".

"It is Twitter's executives that are under federal investigation," he said. Twitter declined to comment on the statement.

The filing comes as the months-long saga of Musk's proposed Twitter acquisition continues, in which the billionaire proposed a takeover, backed out of the deal, and was then sued by Twitter to keep his word. The billionaire's side then announced that he would proceed with the deal, just days before a trial to force the purchase.

Musk vs. Twitter 

Earlier this month, Musk proposed to Twitter that he would move in a different direction and abide by his April agreement to buy all of Twitter's shares for $54.2 each if the company drops its lawsuit against him.

Musk's proposal conditioned that the deal closing was pending the receipt of the necessary debt financing. According to the source that requested to remain anonymous, the potential deal would likely remove that condition.

His lawyers and Twitter's legal team informed the judge of their attempts to try to overcome mutual distrust and find a way to close the deal.

Shares of Twitter closed down 0.7% at $51.63 on October 5 afternoon. On October 4, the stock hit its highest level since Musk and Twitter agreed that he would buy the company in April.

In July, Musk walked away from his $44 billion buyout deal because of repeated violations of the agreement, as he claimed, adding that Twitter did not provide adequate information on the quantity of spam and false accounts.

Part of Musk's case was based on claims by Twitter whistleblower Peiter Zatko that became public in August.

Twitter's legal team has wanted to look into whether Quinn Emanuel's lawyer Alex Spiro, communicated with the whistleblower as early as May. The law firm said in court filings its lawyers did not communicate with Zatko or his representatives.

According to court documents, Twitter unveiled an anonymous May 6 email to Spiro from "a former Exec at Twitter leading teams directly involving Trust & Safety/Content Moderation," who offered to communicate "via alternate means."

Zatko, better known as "Mudge", who headed Twitter security before being fired in January, denied under oath having communicated with Musk or his attorneys at Quinn Emanuel.

The judge, Chancellor Kathaleen McCormick of Delaware's Court of Chancery, said in a Monday ruling it is "at least plausible" Mudge sent the anonymous email. She ordered Spiro to file a statement with the court clarifying his actions regarding the May 6 email.