The Department of Justice dropped a sizable case against a Massachusetts Institute of Technology professor it had accused of hiding millions of dollars in contracts with China while he was getting paid to do research for the U.S. government.

Gang Chen, who came to the United States from China in 1989 and was naturalized in 2000, was arrested a year ago and charged with wire fraud, failing to file a foreign bank account report, and making a false statement in a tax return in connection with undisclosed contracts from “various entities in the People’s Republic of China to the U.S. Department of Energy.”