Since the Crusades we had about a hundred popes, but the one to suffer the assasination attempt just coincidentally also bothered the international Left.
It is possible that Gen. Jaruzelski indeed believes that theory, but he better have something more convincing than "Zhivkov said so". It would be natural for the KGB to keep the religious Poles in the dark and use a Bulgarian ruse. Agca is a classic manipulated killer, and we may never know who manipulated him, but to suspect a retaliation for the Crusades is just silly. The fact that Agca is alive points to the high probability that he himself does not know who planted that thought in him. But he just doesn't look like an Islamic crazy.