The CEO of Tesla and SpaceX will testify this week in a defamation suit brought against him by Vernon Unsworth, a British man who helped with the rescue of 12 boys and their soccer coach from a flooding Thai cave in July 2018. Unsworth is suing Musk for accusing him of being a pedophile and is seeking punitive and compensatory damages.

The trial begins on Tuesday at a federal court in Los Angeles and will presumably reveal more information about the tweets, the Thai cave rescue and Musk's life. Musk and Unsworth are both expected to testify, their respective lawyers told CNN Business. In October, US District Judge Stephen Wilson rejected Musk's attempts to dismiss the lawsuit. Wilson also ruled against classifying Unsworth as a public figure, which now makes defamation easier to prove.

What began as a public spat on Twitter transformed into a much larger problem for Musk. The 48-year-old billionaire had doubled down on the claim against Unsworth on Twitter and in an exchange with a BuzzFeed News reporter Ryan Mac. This lawsuit is far from Musk's first controversy stemmed by his Twitter behavior. In September 2018, Musk agreed to a settlement with the US Securities and Exchange Commission after he tweeted "funding secured" for taking Tesla private.

The timeline

Musk involved himself in the Thai cave rescue by creating a miniature escape pod . On July 8, 2018, Musk tweeted, "Mini-sub arriving in about 17 hours. Hopefully useful. If not, perhaps it will be in a future situation."

When asked about Musk's submarine in an interview with CNN after the rescue, Unsworth said Musk "can stick his submarine where it hurts." Unsworth called Musk's effort "just a PR stunt."

On July 15, 2018, Musk referred to Unsworth as "pedo guy" in a now-deleted tweet. Musk provided no justification or proof to back up his claim at the time. He also responded to a Twitter user who called out the disparaging claim with, "bet ya a signed dollar it's true," which also has been deleted. Shortly thereafter, Unsworth said he was considering taking legal action against Musk.

On July 18, 2018, Musk apologized to Unsworth in a series of tweets, saying "his actions against me do not justify my actions against him, and for that I apologize to Mr. Unsworth and to the companies I represent as leader. The fault is mine and mine alone."

On August 28, 2018, Musk revived the controversy. A Twitter user, Drew Olanoff, tweeted, "your dedication to facts and truth would have been wonderful if applied to that time when you called someone a pedo," to which Musk responded , "You don't think it's strange he hasn't sued me? He was offered free legal services."

BuzzFeed News reported the next day that Unsworth had retained counsel and sent Musk a letter earlier that month notifying him a potential lawsuit.

Days later, in an email Musk sent to Ryan Mac, the reporter behind the BuzzFeed News story, he renewed his original claims against Unsworth. He wrote, "stop defending child rapists," in reference to Unsworth and also accused him of moving to Thailand for a child bride. Unsworth's lawyer described the claims "vile and false."

"Elon Musk falsely accused Vern Unsworth of being guilty of heinous crimes," Unsworth's attorney L. Lin Wood said in a statement at the time. "Musk's influence and wealth cannot convert his lies into truth or protect him from accountability for his wrongdoing in a court of law."

Unsworth, who is a UK citizen, filed the lawsuit in a federal court in California.

The case

A jury will now decide whether Musk was negligent by failing to use reasonable care to determine the truth or falsity of his comments about Unsworth.

Musk had argued that Unsworth's involvement in a high-profile rescue mission made him a public figure, a status that meant Unsworth would also have to prove that Musk acted with "actual malice." But since Judge Wilson tossed out Musk's First Amendment defense that he was engaging with a public figure, Unsworth could succeed with the defamation claim without having to prove actual malice.

Unsworth's defamation suit is focused on the tweets Musk published in July. The case previously also listed the emails with BuzzFeed, but Unsworth's legal team pulled them from the suit and instead petitioned to use them as supporting evidence. The judge ruled on Wednesday the emails can be used as evidence of "establishing Musk's state of mind at the time of the alleged defamation." Unsworth must prove actual malice in order to be awarded punitive damages and Musk's state of mind may be key evidence in proving these damages.

"The crucial issue in the case, for the jury, is going to be to decide whether Musk's use of the term 'pedo guy' in his July 15th tweet was written such that it conveyed to the reader that it was an assertion of fact," Wood told CNN Business.

Musk's lawyer will look to classify the use of "pedo guy" as an insult or opinion, not a statement of fact. In court document filed in September, Musk defended his use of "pedo guy" as a "common insult used in South Africa when I was growing up. It is synonymous with 'creepy old man' and is used to insult a person's appearance and demeanor, not accuse a person of acts of pedophilia."

In that same filing, Musk defended his decision to double down on the claim, sharing how he hired a private investigator to probe Unsworth and blamed the PI for allegedly giving him bad information.