Nosenko was a KGB agent who approached some glowies in 1962, because Nosenko had a problem that he thought the glowies could solve. You see, Nosenko had been given a certain amount of travel money that he was expected to account for when he returned to Russia. But Nosenko, being Nosenko, had spent that money on hookers and booze. He needed to make that money back quickly, so he sold a little information to the glowies, who politely paid his bills for him. Nosenko returned to Russia.
However, now that Nosenko was a traitor, his guilty conscience began to weigh on him. Also, he didn't like his wife very much. Plus, he noticed as he traveled outside the USSR on business, that there was a lot more money, booze and hookers OUTSIDE the USSR than there was IN it. So, he spent two years gathering information and making plans, and in 1964, he received a second opportunity to travel outside the USSR and promptly defected.
At first, the glowies were very happy with Nosenko, because he outed a lot of double agents around the world and gave them a lot of useful information. However, it became apparent that Nosenko was boisterous, crude, drunk, and very fond of hookers. The glowie handlers were afraid he would get himself arrested by the local cops for being a drunk Russian asshole, so they kept him imprisoned in a secure location until 1967--3 years.
During this time, they subjected Nosenko to various interrogations, polygraph tests, good cop/bad cop routines, and noticed certain inconsistencies in his stories, which led to even more interrogations. However, the majority of the information he'd given checked out, and the majority of his polygraphs were clean.
You see, Nosenko, being Nosenko, told a number of grandiose lies about himself that were designed to make him look like a better person than he really was. He was fond of Ghost-of-Kiev type hero stories, as well as glossing over some of the more embarrassing parts of his history, such as failing out of college. After three years of grilling him about every detail of his story, they decided that Nosenko actually was who he said he was, and although he was a known liar, he hadn't lied about anything genuinely important. As a result, after the 3 years was up, they treated Nosenko to a vacation in Florida and bought him plenty of booze and a couple hookers to make up for his poor treatment. The end.
