I just asked myself, and I responded that eyewitness testimony is only as reliable or unreliable as the witnesses themselves.
Any witness who would refuse to recant his testimony in the face of torture or death must be considered as a reliable witness. There you have the circumstantial evidence which confirms the veracity of the eyewitnesses. Where is your evidence to refute the veracity of their testimony? I don't think you have any.
BTW, where did you get your law degree?
So Julius and Ethel Rosenberg show that communism is true?!
Or the sodiers who went into hiding and refused to give up (sometimes for many years) show that Japanese militaristic emperor worship is true?!
There were martyrs for Gnosticism, Catharism, and any other heresy you can think of. There were martyrs for the Aztec religion.
Bottom line, the existence of martyrdom shows absolutely nothing about the credibility of the belief.