The most shocking part of HBO's Theranos documentary, 'The Inventor,' according to director Alex Gibney

• HBO's "The Inventor" takes a look inside the rise and fall of the blood-testing startup Theranos.
• Director Alex Gibney talked to Business Insider about the things he was most shocked by while making the movie.

Though Oscar-winning filmmaker Alex Gibney has spent a lot of his career exploring stories that focus on the dishonest ("Enron: The Smartest Guys in the Room") and the controversial ("Going Clear: Scientology & the Prison of Belief"), there are still things that shock him while making his movies.

Looking back on doing his latest HBO documentary, "The Inventor: Out for Blood in Silicon Valley," Gibney still can't get over how driven the movie's main subject, Theranos founder Elizabeth Holmes, was about denying that she committed fraud.

"It testified to one of the really interesting psychological dimensions of the story, which is most people who are good at telling a fraudulent story are good because they believe it's true," Gibney told Business Insider. "They convince themselves that they are noble."

In June, Holmes was indicted on wire fraud charges (she has pleaded not guilty) and stepped down as the CEO of the blood-testing startup. Investors have lost hundreds of millions since the company shut down in September.

But that wasn't the only surprise Gibney had on this movie.

As Holmes became a self-made billionaire on paper - thanks to the perception of what Theranos could become - she was able to enlist the talents of a heavyweight lawyer to watch her back. That lawyer was David Boies, who was also a Theranos board member. Gibney said when Boies was in the picture at the company it was very difficult for anyone who was involved there to agree to talk for the movie.

"They were afraid that he was going to sue them into oblivion," Gibney said. "That was really hard for somebody who is trying to understand what happened inside a company."

The movie shows just how intimidating Boies' tactics were. One scene looks back on the five-hour meeting Wall Street Journal reporter John Carreyrou (who wrote the book "Bad Blood," which was a source of a lot of the insight that's in the movie) had with Theranos executive Daniel Young, who at the meeting was flanked by Boies and Theranos' general counsel, Heather King. We hear the recording Carreyrou took of the interview as both sides go back and forth about sourcing and accusations of Carreyrou wanting trade secrets.

Read more: The Stanford professor who rejected one of Elizabeth Holmes' early ideas explains what is was like to watch the raise and fall of Theranos

Gibney said things finally got easier when it became clear Theranos was on the ropes and didn't have the resources to take anyone to court who spoke out.

"Despite the good that people could do by coming forward, they were so terrified that their lives would be destroyed by a lawyer that they kept silent," Gibney said. "That was really interesting to me."

"The Inventor" is currently available to stream on HBO GO/NOW.