First, it was a plan from the beginning. We see that in the fact that Jesus celebrated Passover and gave the unleavened Passover bread to His disciples and said, "This is My Body. We see that in Isaiah 53 as well.
Second, Jesus Predicted His resurrection many times Himself before He ever died. Some try to say Jesus did not die. But they are totally missing the point of God's plan of redemption. Jesus said, "Destroy this temple, and in three days I will raise it up." He was talking about the temple of His body. John 2:19-23.
Third: There were many witnesses that testified even in danger. At first the disciples were afraid of those who crucified Jesus. Then they became bold after they knew He had risen. Their amazing boldness along with their willingness to suffer is written clearly in the book of Acts. Read chapters 1-5. To look at one verse, Acts 4:33, "33 With great power the apostles continued to testify to the resurrection of the Lord Jesus. And God’s gracewas so powerfully at work in them all".
Fourth: Those testifying of the resurrection were willing to suffer for that truth because they knew it was true. If it had not been true, then one of the disciples would have revealed the "lie", but they were all consistent in their testimony. This truth has changed history. Read about the amazing testimony of Chuck Colsen as evidence that Jesus rose again.
Fifth: Even His enemies testified that the grave was empty. They paid soldiers to lie and say that His body was stollen by His disciples. This was an excuse to explain why the tomb was empty. So the tomb was empty, but His disciples could not have stollen it. They were too weak and afraid, and in addition, among them, someone would have spilled the beans.
Sixth: Look at the example of Peter. He was afraid and denied knowing Jesus three times during the time Jesus was suffering. But after Jesus rose and spoke to Peter as the living Christ, Peter knew for sure Jesus was alive. He became very bold. When he was beaten for preaching that Jesus was alive, He rejoiced at the previlege to suffer for His Savior. Acts 5.