Three Chinese students are under investigation over footage captured by a drone of a United States aircraft carrier and naval facilities in South Korea in June, local police said on Wednesday.

The suspects are aged between 30 and 49 and are studying in Busan, a port city located on the southeastern coast of South Korea, where U.S. Navy aircraft carriers frequently visit.

The Chinese nationals were caught flying a drone toward South Korea’s Naval Operations Command in Busan where aircraft carrier USS Theodore Roosevelt was docked on June 25, local police said. They are accused of illegally filming the vessel and military facilities.