Over 15 million Chinese have signed an open letter calling on the World Health Organization (WHO) to investigate the U.S. Army Medical Research Institute of Infectious Diseases at Fort Detrick. Published on July 17, the petition appealed to the WHO to investigate the lab and urged the U.S. to answer to the call from people around the world.

So, what is the U.S. Army Medical Research Institute of Infectious Diseases at Fort Detrick? How terrifying is the history of the mystery lab? This video explains.