Nosenko's case officer, both when met in Geneva initially in 1962 and subsequently when he defected in 1964, was Tennent H. "Pete" Bagley. Bagley, subsequently chief of counterintelligence for the Soviet Russia ("SR") Division and Division Deputy Director, wrote a book that was substantially about the Nosenko case. CIA operations officer George Kisevalter, well regarded for his prior handling of Major Pyotr Popov, the first Soviet GRU officer run by the CIA, and a native Russian speaker, was detailed to assist Bagley.
Nosenko contacted the CIA in Geneva, when he accompanied a diplomatic mission to that city in 1962. Nosenko offered his services for a small amount of money, claiming that he had spent KGB funds on alcohol and was therefore desperate for cash. He claimed to be deputy chief of the Seventh Department of the KGB, and provided some information that would only be known by someone connected to the KGB. He was given the money he requested and told $25,000 a year would be deposited in an account in his name in the West. Then, at a meeting set up in 1964 he unexpectedly claimed that he had been discovered by the KGB and needed to defect immediately. Nosenko claimed that the Geneva KGB residency had received a cable recalling him to Moscow and he was fearful that he had been found out. NSA was later, but not at the time, able to determine that no such cable had been sent, and Nosenko subsequently admitted making this up to persuade the CIA to accept his defection, which the CIA did.
The situation was made more complex by another defector, controlled by the FBI, codenamed Fedora. Fedora confirmed Nosenko's story about Oswald. Fedora, however, was eventually seen to be a double agent for the Soviets. Realizing that Fedora was feeding information that the Soviets wanted fed doubt about Nosenko, but did not prove Nosenko was lying, since double agents often provide some accurate information to prove their credibility.
Two lie detector tests conducted by the CIA suggested that Nosenko was lying about Oswald. Moreover, Nosenko confessed that he had lied to the CIA about his military rank.
When the interrogations led to no substantial results the interrogators were changed and after bringing on a new team Nosenko was cleared of all suspicions and released with pay. The question of whether Nosenko was a KGB plant or not is controversial, and those who handled him initially still believe that his unsolicited walk-in was designed by the KGB to protect a Soviet mole threatened by Golitsyn's knowledge, and his defection by a Soviet desire to discredit the idea of a connection between the Soviet Union and the actions of Lee Harvey Oswald. Others have argued Nosenko was ultimately regarded as an authentic defector through misinformation from another KGB-agent that was thought to be a genuine defector, code-named Fedora.
Nosenko has later claimed to have been tortured and even at one point, he said, he was given LSD, and it almost killed him. The guards revived him by dragging him into the shower and alternating the water between hot and cold. These claims have been denied by Richard Helms who was DCI during the most intense part of Nosenko's interrogation. LSD is generally considered nontoxic.
It has been claimed that it was the CIA counter-intelligence chief, James Jesus Angleton, who was responsible for the hostile interrogation. Angleton did favor Golitsyn in the disputes with Nosenko, but all those involved in the case at the time, including both of Nosenko's handlers, Tennent Bagley and George Kisevalter, agree it was the SR-division. The case has been examined in several books, and the 1986 movie "Yuri Nosenko: Double Agent" starring Tommy Lee Jones. The movie depicted the intense debate over whether Nosenko was an actual defector.
Former CIA case officer Robert Baer wrote that "when Nosenko offered a version of Lee Harvey Oswald and the Kennedy assassination that didn't fit with the agency's corporate view he was sent to solitary confinement at the farm for three years."
He helped expose John Vassall, a British civil servant, charged with spying in 1962.
Until his death, Nosenko lived in the US under an assumed name.