Why did false-defector Yuri Nosenko say KGB didn't even interview Marine Corps radar operator Oswald? (John Newman believes they interviewed him at least twice.)
Probably because Nosenko wanted to get on CIA's and FBI's "good side" so he could more effectively contradict what true-defector Anatoliy Golitsyn was telling them about KGB/GRU penetrations of U.S., Canadian, and our European allies' intelligence services, and, of course, about "The Monster Plot," in general.
It may also have been because Oswald was recruited by the KGB, either before or while he was in the USSR,
for a completely different reason, and KGB intuited (correctly, thanks to the actions of Leonard McCoy and John L. Hart, et al.) that after CIA and FBI had breathed a collective sigh of relief regarding any Soviet involvement in the assassination, neither of those agencies would want to risk opening any potential "can of worms" involving Oswald, period.
This interpretation might help to explain why Nosenko didn't say, "Well, yes, we did interview him once or twice, but we decided he was of no value to us," but instead "went over the top" and said, "Nope, he was so crazy and 'loose cannon'-looking that not only did we not interview him, heck, we didn't even
monitor him during the two and one-half years he lived with us."
-- MWT