SeaBreeze Acts 2:32 says God resurrected him.
@enoughisenough - Exactly, that is how he did it. In John 2: 19 Jesus predicted that he would provide a sign to the Jews so dramatic, that only God could do it. It was a feat that no one has ever before or since duplicated. In John 10: 17-18 Jesus predicts that he would perform the same feat, although for slightly different reasons.
The fact that there is no evidence that he resurrected himself.
@TonusOH - Just pretend that there was evidence for a moment; do you think you would trust Jesus with your eternity? In other words, would a self-resurrection from the dead be enough of a demonstration for you to trust him?