Martyrdom of Peter and Paul as evidence for the sincerity of resurrection belief

The disciples were willing to die for their testimony that Jesus rose from the dead. Particular documentation exists for Peter and Paul: Clement of Rome's letter to the Corinthians records both Peter's and Paul's martyrdom. John 21 — Jesus predicts Peter's death by crucifixion; if John wrote near the end of the first century, it is unlikely he would attribute a false prediction to Jesus. Origen records that Peter was crucified upside down — he didn't feel worthy to die the same way as his Lord. This is all the more striking because Peter had previously denied Jesus three times to save his own skin. Something dramatically transformed Peter.