Sunny Balwani, former president and chief operating officer of Theranos Inc., leaves federal court in San Jose, California, Oct. 2, 2019.Sunny Balwani, former president and chief operating officer of Theranos Inc., leaves federal court in San Jose, California, Oct. 2, 2019.

He was the man behind the lab curtain. He is in the middle of his own criminal fraud case.

The trial of the former president and COO of Theranos begins Wednesday in the San Jose federal courthouse.

The fate of Balwani will be decided by a jury of men and women. Each has a maximum penalty of 20 years in prison. He denied the charges.

She could be a key witness against Balwani while she is sentenced in September. Balwani was also the No. 2 executive at Theranos.

She told the jury that Balwani had a pattern of sexual and psychological abuse, which had an impact on who she was. Balwani denied the allegations.

Reed Kathrein, an attorney who represented some investors in a lawsuit against Theranos, told CNBC that Balwani was central to the ruse, which involved lying about the company's technology and bilking shareholders out of hundreds of millions of dollars.

Kathrein, who isn't involved in Balwani's criminal fraud case, said thatSunny ran everything.

Widespread publicity surrounding the case delayed opening arguments. It took close to 100 candidates four days to be questioned by a jury.

More than half of the potential jurors raised their hands when asked if they had heard about Theranos. Several people said they had knowledge of abuse claims against Balwani.

After she served as the main witness in her own trial, prosecutors haven't said if they will call her back to the stand. Kathrein said that she could testify against Balwani in order to reduce her sentence.

Kathrein said that Elizabeth wants to throw him under the bus. She did it again at her trial. I would not be surprised if she testifies to save herself from a harsh sentence and throws him under the bus again.

Jeffrey Coopersmith, Balwani's attorney, declined to comment. CNBC asked for comment from attorneys forHolmes, but they didn't reply.

Theranos founder Elizabeth Holmes, center, and her family leave the Robert F. Peckham Federal Building and U.S. Courthouse after the jury found her guilty on four counts in San Jose, Calif., on Monday, Jan. 3, 2022.

Balwani, a former software executive who made millions during the dot-com boom, met Holmes in Beijing, where they were both studying Mandarin. It was the summer before the freshman year at the university. He was 37 when she was 18.

After starting Theranos, he dropped out of school. They moved in together in Palo Alto, California, in 2005. Their 12-year romance was kept a secret from their business partners and employees.

Balwani began his involvement with Theranos in 2009. Balwani provided a $13 million loan to the company. He became president and COO six months later.

Balwani advised her on how to run a company. She testified that she believed Balwani to be a successful businessman and that he worked for Bill Gates.

The most dramatic moment of her trial was when she described Balwani's controlling behavior. She told the jury that Balwani dictated her schedule and diet. She stopped short of blaming Balwani, but she did say that he never told her what to say to investors or pharmacy partners.

He wasn't who I thought he was and I had to fix it.

After an inspection from regulators revealed major problems inside the Theranos laboratory, ElizabethHolmes moved out of the Silicon Valley home they shared. Balwani left Theranos.

The Securities and Exchange Commission charged Balwani and Holmes with massive fraud in March of last year, but Balwani rejected the settlement and is fighting the charges separately.

Danny Cevallos, an attorney and NBC News legal analyst, said that Balwani is at a disadvantage because he has already been convicted. CNBC obtained text messages from the trial that show Balwani was involved with the company's daily operations.

Cevallos said that the government figured out what worked and what didn't. This case is even more airtight because of that.

Barbara McQuade is a former U.S. attorney.

McQuade, who is also an NBC legal analyst, said that the defense usually has an advantage when it is the second time through a case. A good defense attorney will point out the inconsistencies to the witness to show that his memory is unreliable.

McQuade said prosecutors may prefer not to call her because she is a known fraudster.

Cevallos sees the reason for keeping Holmes off the stand.

The government knows what a convincing person Elizabeth is. They have already won a case without her, and they probably don't want her to get off lighter than Balwani.