Liu Ruopeng — known as China's Elon Musk — studied at Duke University from 2006 to 2009 under David Smith, one of the world's leading experts on metamaterials.

Smith has accused Liu of taking his research and replicating it in China for his own gain.

Some observers, including a former assistant director of counterintelligence at the FBI, believe that Liu was sent to Smith’s lab by the Chinese government.

A Chinese billionaire who studied at Duke University allegedly stole a professor's ideas behind special invisibility technology — and then developed his own prototype back in China.

Liu Ruopeng, known as China's Elon Musk, is just 35 years old and is believed to be worth $2.7 billion, according to the "Today" show.

But before he created his money-making "Future Studio" in China, Liu studied at Duke University from 2006 to 2009 under David Smith, one of the world's experts on metamaterials, or "some weird material that doesn't exist in nature," as the professor describes it.

Some observers, including a former assistant director of counterintelligence at the FBI, believe that Liu was sent to Smith's lab by the Chinese government to steal intellectual property.

Smith had been working on a prototype for an invisibility cloak, and the US military had poured millions into his research.

The invisibility cloak doesn't necessarily make a person disappear, but it makes objects invisible to microwave signals.

At one point while at Duke, Liu convinced Smith to allow him to bring his old colleagues into the lab to work on projects for the professor.

When Smith was out of the lab, the Chinese researchers took photos of the lab and its contents, and also took measurements of Smith's equipment.

Much to Smith's surprise, an exact replica of his invisibility cloak prototype was built in Liu's former lab when the Chinese researchers returned home.

"It sounds like theft," Smith said. "If we were a company you might think so."

Liu claims that his time in the lab was "fundamental research" he brought back to China when he was finished at Duke.

Now, nine years after graduating from Duke with a Ph.D, Liu is a multi-billionaire, the inventor of a jet-powered surfboard, the founder of a $6 billion tech company, and features a prototype of an invisibility cloak in his own lab.

He has denied all wrongdoing, calling the claim that the Chinese government sent him to Duke to learn from Smith "ridiculous" and "far away from the truth."

"I don't want to use the word copy," Liu said. "People can share the experience … and build something … different."

Shortly after Liu graduated in 2009, Smith discovered an email which shows the student admitting he had withheld information from the professor, adding that he had been working toward commercializing the research in China.

Smith told NBC News that if the email had emerged while Liu was still a student, he wouldn't have a degree from Duke.

The FBI opened a case into Liu in 2010 to investigate whether it was theft of US intellectual property.

"We know that certain government officials and operatives met with him while he was in the United States," former FBI Assistant Director for Counterintelligence Frank Figliuzzi said.

He added: "Was he handled, approached, compromised, recruited, and subsidized when he took it back to China? My theory says yes. This was more than just a grad student taking something that didn't belong to him."

The case, however, was closed years later due to shortage of evidence.