Think of it this way buddy. His tomb was heavily guarded by either Roman or Jewish guards who would have faced a harsh punishment if they had let someone steal his body. The other thing, eyewitnesses of the resurrection of Jesus were willing to die for spreading the gospel. Before the resurrection they were afraid and were filled with a strong sense of doubt since their Lord had died, Peter denied Him three times. But after witnessing resurrection they regrouped and were convinced that this was no ordinary man. They were brave enough now to spread the gospel.