Since the bible contains invented prose anyway, it isn't hard to believe the crucifixion of Jesus is also fictional. By that I mean the various miracles attributed to Jesus, which are also found in Indian and Egyptian mythos of the time. In other words, the story is embellished to portray Jesus as divine.
The whole crucifixion story, as well as those of the miracles, runs very close to the mythology of Dionysus/Bacchus. There is not one depiction of the biblical crucifixion prior to the fourth century, and one source I have suggests even later than that. Even the 'donkey on a cross' graffito in the catacombs, believed popularly to be a pagan mockery of Jesus (if so, a far from intelligent one) is nothing of the kind and is a reference to Osiris, whose stories also anticipate many of the Jesus ones. Depictions of Bacchus on a cross, however, are sometimes found, dating from the 2nd century. They even show the very familiar 'slump' of the knees to one side, seen so often in later crucifixes. (yes, I can provide references and pictures if required).
Maybe the crucifixion story was grafted from earlier mythology as a mechanism to make pagan converts feel comfortable with the idea of a deified Jesus. It would not be the only instance of pagan mythology being grafted on to the new faith.