[m1n1]

The involvement of Saul in the stoning of Stephen is generally seen as an established historical event - AD 34-35 - basically within a couple of years of Christ's bodily resurrection.

Many others were killed during the reign of the Roman Emperor Nero (54–68 AD), well within the lifetime of the 500+ eyewitnesses of Christ being around for 40 days after his crucifixion. They could have recanted if they knew it was false, but they knew it was true.