Iowa State University researcher Dong Pyou Han was sentenced to four and a half years in prison for falsifying information on a grant related to his HIV vaccine work, the Washington Post reports. He is also ordered to repay $7.2 million in federal grants his team received from the National Institutes of Health (NIH).

Han, who is a Korean national, resigned in 2013 after it became known that he tampered with HIV vaccine research. Han said that back in 2008, while he was working for researcher Michael Cho on a test involving rabbit blood, some of the rabbit blood became contaminated with human blood. Instead of admitting the error to Cho, he contaminated future samples. The resulting data for vaccine GP41 looked promising and led to future grants.

Han’s dishonesty was discovered when other scientists tried to duplicate Cho’s results and examined the rabbit blood samples from Cho’s lab.

Initially, Han was banned from applying for grants for three years and the university repaid the $500,000 it had received from the NIH for Han’s salary. But when U.S. Senator Charles Grassley (R-Iowa) wondered why the sentencing was so light, federal prosecutors took up the case and made an example of Han.