Of course a historical Jesus may have existed, perhaps based loosely on a living human even though his actual history got lost, but this amounts to nothing but speculation. However we do have an abundance of evidence supporting the mythical evolution of Jesus. Virtually every detail in the gospel stories occurred in pagan and/or Hebrew stories, long before the advent of Christianity. We simply do not have a shred of evidence to determine the historicity of a Jesus "the Christ." We only have evidence for the belief of Jesus.
So if you hear anyone who claims to have evidence for a witness of a historical Jesus, simply ask for the author's birth date. Anyone who's birth occurred after an event cannot serve as an eyewitness, nor can their words alone serve as evidence for that event.