Well, that's kind of the point. All we have is one account, written by those who want to put Jesus in a good light and to emphasize the supremacy of the new religion over the others.

Considering what we've seen with regard to government over the years, though, it's not hard to imagine the possibility that the Romans were worried about rioting or political instability. Even by the book's own account, Pilate asked several times for someone to produce some hard evidence that Jesus was advocating for overthrow. All he got in response was more hearsay and an increasingly unquiet mob outside his courtroom. Over the course of the trial, things got bad enough that he released a known terrorist instead of the innocent man when it came time for the annual pardoning. Otherwise, he might have had a riot on his hands all across Judea.

There's no account of Pilate's side of the story, though, so we have no idea what he and the Romans thought of the strange man that was gathering a following, intentionally or not. All that is mentioned is that the Judean was brought to a trial, Pilate shrugged and asked for evidence, and in return got a threatened riot. I can't say that this side of the story is correct, but it is possibly true. Including all of the stuff that would confirm or deny in the Christ-story, however, doesn't accomplish anything toward promoting the underlying message of Jesus, so it's not there.

I was aiming for a telling of the story and the history of the churches up to today from a perspective somewhere outside the believer's mindset.