John Hanlon was one of eight FBI agents involved in a shootout considered to be "The Bloodiest Day in FBI History." This event took place on April 11, 1986, in south Dade County, Florida, just outside of Miami, when the agents engaged William Matix and Michael Platt, responsible for a series of bank and armored car robberies (not to mention injuries and murders) in a firefight. Both Matix and Platt were killed, as were agents Ben Grogan and Jerry Dove. In addition to Hanlon, agents Gilbert Orrantia, Richard Manauzzi, Gordon McNeill, and Edmundo Mireles were also injured. Only agent Ronald Risner escaped injury. Following this incident, the FBI made changes in training, body armor and weapons.