Vernon Unsworth, who has denied the allegations, chose to pursue liability and damages claims at a scheduled Dec. 3 negligence trial only for Musk's tweets allegedly calling him a paedophile, U.S. District Judge Stephen Wilson said in a Wednesday order.
The judge also decided not to split up the trial to assess liability and punitive damages separately because evidence of Musk's "state of mind" would be similar on both issues, and Musk refused to concede he did not use reasonable care in criticising Unsworth.
Alex Spiro, a lawyer for Musk, declined to comment on Friday. Unsworth's lawyer, L. Lin Wood, did not immediately respond to requests for comment.
Wilson issued his order after hearings this week in Los Angeles. Musk is expected to testify at trial.
The case arose after Unsworth and his diving team gained international renown in July 2018 by rescuing 12 boys and their soccer coach from a Thailand cave.
Unsworth criticized Musk's offering a mini-submarine from his SpaceX rocket company to help with the rescue, telling CNN it was a "PR stunt" and that Musk could "stick his submarine where it hurts."
But he said that did not justify Musk's July 15, 2018 tweets that he "never saw this British expat guy," followed by "Sorry pedo guy, you really did ask for it" and, in an alleged clarification, "Bet ya a signed dollar it's true."
Wilson said Unsworth chose not to pursue damages claims over later emails by Musk to BuzzFeed News, including that a reporter "stop defending child rapists."
The judge said Unsworth can use those emails to show Musk's state of mind behind the July 15 tweets. Musk has apologised for the "pedo guy" comment.
To win, Unsworth must show the tweets were false, Musk did not use reasonable care to determine their truth, and people reasonably understood them to mean Unsworth was a paedophile.
Wilson said he will admit evidence suggesting that Musk might have leaked damaging information about Unsworth to the press, and Unsworth might have sued to capitalise on his fame.
Evidence of Musk's $20 million civil settlement with the U.S. Securities and Exchange Commission in 2018 after he tweeted that Tesla had "funding secured" to go private was excluded because it might confuse jurors.
By Jonathan Stempel
