Complex sentence: The "Penkovksy Papers" were alleged to have been written by a Soviet GRU defector, Colonel Oleg Penkovsky, but was in fact produced by the CIA in an effort to diminish the Soviet Union's credibility at a pivotal time during the Cold War.
Split into simpler sentences: The "Penkovksy Papers" were alleged to have been written by a Soviet GRU defector, Colonel Oleg Penkovsky. The book was in fact written by the CIA in an effort to diminish the Soviet Union's credibility at a pivotal time during the Cold War.