Elon Musk’s erratic behavior of late has worried investors and Tesla Inc.’s board of directors, and his latest tirade is unlikely to ease those concerns.

In a series of emails to a reporter published Tuesday by Buzzfeed News, Musk doubled down on his personal attack against a British man who helped in the rescue of a youth soccer team trapped in a cave in Thailand, calling him without basis a “child rapist” who took “a child bride who was about 12 years old at the time,” adding that he welcomes a lawsuit. Musk also called a Buzzfeed reporter an expletive.

“ “I f***ing hope he sues me.” ” — Elon Musk, in an email to Buzzfeed

Musk had previously called the British cave-diving expert, Vernon Unsworth, a “pedo” in a tweet, then apologized, and Unsworth’s lawyer threatened in August to sue the Tesla chief executive for libel.

In the Buzzfeed emails, Musk also questioned Unsworth’s expertise and role in the rescue effort, again apparently without evidence to back his claims.

Read:Elon Musk is more famous than ever, and maybe more dangerous

In July, Unsworth dismissed the mini submarine that Musk sent to Thailand as a publicity stunt, and said it would be useless in the rescue effort. But it is unclear why Musk has repeatedly and publicly attacked Usworth, 63, since then — or where the apparently baseless pedophilia allegations came from.

“Elon Musk can tweet his vindictive and vicious lie about Mr. Unsworth a hundred times and it will still be a lie,” Unsworth’s lawyer, L. Lin Wood, told Buzfeed in a statement. “After deleting the initial accusation and tweeting an apology, Mr Musk has continued to republish his false and unsupportable accusation. His conduct demonstrates that his recklessness is intentional and designed to harm Mr. Unsworth.”

Tesla had no comment, according to a spokesperson.

Last month, Musk told the New York Times that he was experiencing an “excruciating” year, and the Times reported that Tesla’s board members were worried about his health and well-being, as well as his use of the sleep aid Ambien. Musk has ramped up his social-media activity this year — often to his detriment. — and in August denied accusations from pop star Azealia Banks that he tweeted while high on drugs.