We have independent traditions, eyewitness accounts, unadorned by later theological sophistication, that give us primary evidence. Those Gospels provide remarkably little detail (Mark 14.51-52), often give a bad press to the first followers (doubting Thomas, Peter the denier), and can sometimes seem hard to reconcile (just how many times did the cock crow when Peter denied Christ?). Actually all this points to their authenticity. Of course, apparent contradictions can be resolved – they are only apparent – but their existence only serves to confirm that we have independent traditions. If four witnesses to a criminal act all gave an identical story then we might suspect collusion!