He was a KGB agent, a Soviet defector who’d come to the United States in January 1964, just two months after President John F. Kennedy’s assassination. Yuri I. Nosenko, a former lieutenant colonel in the Soviet secret police and intelligence agency, told his new American friends that he had important information: He had handled Lee Harvey Oswald’s KGB surveillance file during his time in the Soviet Union in the late 1950s and early 1960s — and determined that Oswald had nothing to do with Kennedy’s assassination.
By 1966, Richard Helms, then the agency’s director of operations, ordered the CIA to make a call on Nosenko’s truthfulness. The KGB agent wound up passing multiple polygraphs and, by 1969, was released. Finally, the CIA believed him. He even became a consultant to the agency, but was given a new identity and home somewhere in the South.