Elon Musk, chief executive officer of Space Exploration Technologies Corp. (SpaceX) and Tesla Inc., speaks during an event at SpaceX headquarters in Hawthorne, California, U.S., on Thursday, Oct. 10, 2019.Patrick T. Fallon | Bloomberg | Getty ImagesTesla and SpaceX CEO Elon Musk is testifying in a defamation trial in Los Angeles Tuesday, after he defamed a British spelunker, Vernon Unsworth, who is best known for his efforts to rescue 12 boys and their soccer coach from flooded caves in Thailand in the summer of 2018. Musk arrived in court after noon PT and is expected to be the first witness when testimony resumes after 1 p.m.Unsworth filed the lawsuit in the U.S. in September 2018.The conflict began when Unsworth criticized Musk for his efforts to involve himself in the Thai cave rescue.Musk and his employees developed a mini submarine, which they billed as an escape pod that could transport the kids out of the caves. On July 8, 2018, Musk wrote in a tweet, “Mini-sub arriving in about 17 hours. Hopefully useful. If not, perhaps it will be in a future situation.”The sub was never used in the rescue effort. After the rescue, Unsworth was asked about the mini-sub and Musk on an interview with CNN. He said that Musk could “stick his submarine where it hurts,” and viewed Musk’s efforts as “just a PR stunt.”Lashing back after that, Musk called the caver a “pedo guy” in public tweets, and “child rapist” in an email to a reporter at Buzzfeed.Musk and his defense team have claimed that “pedo guy” tweet, which Musk later deleted, was meant an insult tantamount to “creepy old man,” and did not constitute defamation. According to CNBC’s Jane Wells, who was in attendance at the trial, jury selection proved challenging but not impossible in Los Angeles, which is both a design headquarters for Tesla, and a massive market for the electric car company.Of a panel of around 40 prospective jurors, at least four said they owned Tesla vehicles, six said they had done business or owned shares in one of Elon Musk’s companies (including the tunneling startup the Boring Company), one said they were interviewing for a job with SpaceX, and two said they followed Musk on social media and felt they could not remain impartial.The presiding judge, Hon. Stephen V. Wilson, asked the first eight prospective jurors in the box if they had strong feelings about billionaires or people who live in or travel to Thailand. He said the case hinges on whether a reasonable person, given context, would take the phrase “pedo guy” to mean Mr. Musk was calling Mr. Unsworth a pedophile.Ultimately Musk’s attorney Alex Spiro, and Unsworth’s attorney L. Lin Wood, and the judge agreed on a jury of three men and five women, of multiple ethnicities who ranged in age from their 30s to their 70s. Most were college educated.Spiro, in his opening statements, said that the case was “about insults not statements of fact.” He said Musk’s tweets were “not allegations of a crime,” but only “joking taunting tweets in a fight between men.”This is a developing story. Please check back for updates. Follow @CNBCtech on Twitter for the latest tech industry news.