(AP) — A high-profile trial focused on a 2018 tweet about the financing for a Tesla buyout that never happened drew a surprise spectator Friday — Elon Musk, the billionaire accused of misleading investors with his usage of the Twitter service he now owns.

Musk, the CEO of both Tesla and Twitter, strode into the San Francisco federal courtroom moments before closing arguments from the opposing attorney in the case were scheduled to begin and took a seat alongside his legal team. Like everyone else in the courtroom, he was wearing a mask, as required by U.S. District Judge Edward Chen, but briefly dropped it as he chuckled and whispered something to one of his lawyers.

Although an August 7, 2018 tweet disclosing he had “funding secured ” is the at the center of the trial, Musk wasn’t required to show up for Friday’s proceedings. His presence in court while he is trying to reverse huge losses at Twitter and overseeing Tesla amid stiffening competition underscores the importance of the trial’s outcome to him.

If the nine-person jury decides to hold him liable for misleading Tesla shareholders during a 10-day period in August 2018 for the funding secured tweet and a follow-up tweet indicating a deal was imminent, Musk and Tesla could be on the hook for billions in damages.

Those 2018 tweets already have cost Musk and Tesla $40 million to settle Securities and Exchange Commission allegations of misconduct. Chen had decided last year that Musk’s 2018 tweets were false and has instructed the jury to view them that way.

During roughly eight hours on the stand, Musk insisted he believed he had lined up the funds from Saudi Arabia’s Public Investment Fund to take Tesla private after eight years as a publicly held company. He defended his initial August 2018 tweet as a well-intentioned communication to ensure all Tesla investors knew the automaker might be on its way to ending its then-eight-year run as a publicly held company.

“I had no ill motive,” Musk testified. “My intent was to do the right thing for all shareholders.”

The jury is expected to begin its deliberations in the afternoon after the closing arguments are finished.