Former Iowa State University researcher Dong Pyou Han leaves the federal courthouse in Des Moines, Iowa, on July 1, 2014. (AP Photo/Charlie Neibergall, File)

Dong Pyou Han, a former Iowa State University researcher charged with falsifying HIV vaccine research, says that his troubles all started as an accident. Quickly, it became a multimillion-dollar research fraud scheme that landed him in prison.

On Wednesday, Han, 57, became a rare academic to not just fall from grace but also be punished with time behind bars.

A federal judge sentenced him to more than four and half years in prison and ordered him to repay $7.2 million in grant funds his team received from the federal government using his falsified data.

Academic misconduct often doesn't even result in researchers losing their jobs, and it is even rarer for criminal charges and prison time to result from one of these cases. In 2006, a researcher pleaded guilty to falsifying information on an NIH grant and was sentenced to a year in prison -- the first time such a sentence handed down for scientific misconduct.

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In 2013, Han, a Korean national, resigned in disgrace from the Iowa university. The U.S. Office of Research Integrity slapped him with a 3-year ban on pursuing federal research grants. And the university repaid the $500,000 it had received for Han's salary from the NIH.

But the case and the scope of the fraud caught the eye of U.S. Sen. Charles E. Grassley (R-Iowa) who demanded to know why more had not been done to recover the millions spent by the NIH to fund the bogus research.

“This seems like a very light penalty for a doctor who purposely tampered with a research trial and directly caused millions of taxpayer dollars to be wasted on fraudulent studies,” Grassley noted in a 2014 letter to the investigatory office that typically levies punishments for this type of misconduct.

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And with that, Han became a cautionary tale. Federal prosecutors pursued criminal charges carrying penalties of up to five years in prison.

"Just because somebody has a PhD, just because someone's involved in the scientific community, doesn't mean they're going to necessarily be treated differently than anyone else who's committed a criminal offense," Nicholas Kleinfeldt, U.S. attorney for the southern district of Iowa told CNN.

The lies began in 2008 when Han he worked on an HIV vaccine research team lead by Michael Cho, who was then a professor at Case Western Reserve University in Cleveland. Test results from Cho's lab showed that rabbits who were injected with the vaccine GP41 showed signs of antibodies in the blood, suggesting that the vaccine had prompted an immune response against the HIV.

With the seemingly promising research, Cho submitted grant requests to NIH officials who were "flabbergasted," by the results, according to the federal complaint.

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According to Han, the rabbit blood became contaminated with human antibodies, but he realized the mistake too late and never informed Cho. Instead of admitting them, he continued to spike future samples, which gave the impression that the rabbits were mounting an immune response and neutralizing the HIV virus, results that were considered to be a breakthrough in the effort to find a viable vaccine for the virus.

In 2009, Cho was recruited by Iowa State University, and brought Han and other members of his team with him. The HIV vaccine research continued and as more grant money began flowing in, so did efforts by other researchers to validate the results.

That is when Han's problems really began.

As a lab manager, he had direct access to the samples and communicated directly with Cho, helping to supply data for his grant applications, according to the federal complaint. For years, he had apparently been spiking the blood with human antibodies.

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In early 2013, however, researchers at a lab at Harvard University -- trying to validate Cho's team's results -- found something unusual in the rabbit blood samples sent over by Cho's lab: human antibodies.

Cho immediately reported the problem and Iowa State University and the federal government launched an investigation.

Confronted with the findings, Han resigned and took responsibility for the faked results.

In a two-page mea culpa, Han said he was "ashamed" of his misconduct but that it was "not done in order to hurt" anyone.

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In February, he pleaded guilty to two counts of making false statements and admitted to falsifying the data which had been used to garner millions of dollars in federal grant money.

His attorney pleaded with the court for probation, not jail time.

“Here, there is little reason to believe that Dr. Han has not already been deterred from any future criminal conduct. His conduct is aberrational in an otherwise admirable life,” Han's public defender Joseph Herrold wrote, according to the AP. “He regrets the hurt he has caused to his friends and colleagues, the damage he has caused to government funded scientific research, and the pain he has caused any members of the public who had high hopes based on his falsehood.”

And while the case, now closed, clearly sends a warning signal to other potential perpetrators of academic fraud, some wonder whether it was worth it.

“It’s questionable how much more is to be gained by jail time," David Wright, a former director of the U.S. Office of Research Integrity told Nature.