Born in Commack, Long Island, New York on May 9, 1956, Rossi served in the U.S. Marine Corps and made it to the rank of Sergeant Major. While a Private, he served in the Vietnam War under Sergeant Harrison Scott, who he would later refer to as the person who taught him to be honest. During his military service, Rossi earned several awards, including the Purple Heart. When he was younger, he had some association with a local mafia through a good friend named Ray Finnegan, but he severed his ties to them when he left town. He also knew a girl named Emma Louise Taylor ever since he was twelve years old. He loved her, but due to his career, they never married; Emma later went on to marry future judge and proxy killer Boyd Schuller. After leaving the Corps, he was recruited by the FBI. A few years later, he played a part in founding the BAU