And here’s an excerpt from her discussion on the problem of using the Gospels as a historical source:

We already knew that Gibson’s efforts to be “as truthful as possible” (his own words in the Times) would be frustrated by the best sources that he had to draw on, namely, the Gospels themselves. Mark, Matthew, Luke, and John, whose texts were composed in Greek between 70 C.E. and 100 C.E., differ significantly on matters of fact. In Mark, Jesus’s last meal is a Passover seder; in John, Jesus is dead before the seder begins. Mark and Matthew feature two night “trials” before a full Jewish court, and a dramatic charge of “blasphemy” from the high priest. Luke has only a single trial, early in the morning, and no high priest. John lacks this Jewish trial scene entirely. The release of Barabbas is a “Roman custom” in Mark, a “Jewish custom” in John. Between the four evangelists, Jesus speaks three different last lines from the cross. And the resurrection stories vary even more.
The evangelists wrote some forty to seventy years after Jesus’s execution. Their literary problems are compounded by historical ones: it is difficult to reconstruct, from their stories, why Jesus was crucified at all. If the priests in Jerusalem had wanted him dead, Jesus could have been privately murdered or killed offstage. If the priests had wanted him killed but were constrained from arranging this themselves, they could have asked Pilate to do the job. If the Roman prefect had simply been doing a favor for the priests, he could easily have arranged Jesus’s death by any of the considerable means at his disposal (assassination, murder in prison, and so on).
The fact that Jesus was publicly executed by the method of crucifixion can only mean that Rome wanted him dead: Rome alone had the sovereign authority to crucify. Moreover, the point of a public execution, as opposed to a private murder, was to communicate a message. Crucifixion itself implies that Pilate was concerned about sedition. Jesus’s death on the cross was Pilate’s way of telling Jerusalem’s Jews, who had gathered in the holy city for the paschal holiday, to desist from any thought of rebellion.