You're assuming the Book of John was writen by someone other than John.
That's correct, depending on how you define "John". I'm assuming that none of the eyewitnesses produced written documents that survive. Nor do I find it likely that any part of the new Testament was written down at all by any of the eyewitnesses.
There's a lot of talk of love on this thread, but the God described by some here -- as one that would condemn skeptics -- sounds a lot like my image of Satan than of a loving God. I might add that I don't find in the words of Jesus, much demand for theological purity. In my opinionn, the demand for faith in a specific historical interpretation has been tacked on to Christianity by the usual crowd of power hungry hypocrites who always seem to infest churches.