There is no such thing as "proven" with absolute certainty. Even video evidence can be manipulated. The best that we can do is to have a very strongly supported claim, as opposed to weakly supported claims. We can however rule things out using evidence.
The academic field of historiography deals with using valid methodology in determining what in historical documents is true, and what is not. There are several principles that one can point to in this process. Such as:
There are others, including considering how contemporary to the actual events the written account is. (As we know the gospels were written years after Jesus died).
While historiography mainly applies to documents, there are similar principles in the consideration of, for instance, archeological evidence.
In addition to comments posted here, you might find some food for thought in this old thread from a year ago.
I think a great resource to examine is Stanford's "Reading Like a Historian" series. One must examine the primary documents surrounding an event and look for the least of amount of bias as well as corroboration between accounts in order to find the most reliable "history".