We have lots of eye witness accounts. Naturally they became believers because they saw the risen Jesus. The whole death and resurrection of Jesus was very public in a major city, the heart of Israel - Jerusalem. But if you dis-allow eyewithess accounts from believers, then that is poor scholarship. That is not how historical scholarship works.
It's like saying to a court, you can't allow eyewitness testimony of the murder because they are biased, they believe the defendant is a murderer! That's nonsense.
No one says it better than Donnal and Connal.