First note that every claim against the resurrection – whether it be that someone stole it, like the High Priest claimed (Mat. 28:13), or a misplaced tomb, or the infamous "swoon" theory where Jesus didn't really die but only fainted – all of these admit an empty tomb. We have the same evidence; one theory simply tries to avoid Jesus as God and another accepts it. Either way, you have to deal with an empty tomb.
The best theory anyone's come up with for that is mass hallucination, but that can't explain the number of recorded sightings or the interaction they have with him. Even the early Jewish writings against Christians don't claim the body was still in the tomb, but they give naturalistic explanations for the tomb being empty. So we can know for certain, absolutely certain, that the tomb wherein they laid Jesus after the crucifixion was empty beyond a doubt.
We even have an anti-Christian historian in 66 AD who writes that "Jesus' disciples reported that he had appeared to them three days after his crucifixion and that he was alive; accordingly, he was perhaps the Messiah" (Josephus, Antiquities). 2nd Century apologist Justin Martyr claims to have seen Pilate's documents to the emperor about Jesus, but these have not yet been found. Though we have found a stone bearing Pontius Pilate's name in Palestine, proving he really was the governor there. Amazingly, there's also been found a monument in Nazareth where Caesar, likely Tiberius or Claudius, had inscribed in marble the declaration that anyone who violates a grave by moving bodies or breaking stone seals on tombs would be guilty of capital charges and need their own grave. Why Nazareth, do you think? Why graves and stone seals? Further, the very bones of the high priest, Joseph Caiaphas, who condemned Jesus and started the rumor of the disciples stealing the body have been found and unquestionably identified. For a more in depth treatment of this fabulous evidence, see Dr. Paul Maier's book "In the Fullness of Time: a historian looks at Christmas, Easter, and the early church."
All of the above is, of course, circumstantial, and even the circumstantial evidence of non-biblical sources, especially these many non-Christian sources, makes it clear that Jesus truly existed, truly died, and that three days later the tomb was empty.
If a person claims to be rational, they next must go from the circumstantial to seek the testimony of the eyewitnesses. The Apostles and Evangelists claim that they were these eyewitnesses and they record for us and all who will listen exactly what they saw in their Gospels and in their Epistles. They say that they saw the resurrected Jesus with the nail marks in his hands and feet and the spear mark in his side. They say he ate and drank with them, spoke with them, breathed on them, and that he appeared in this resurrected glory to over 500 others, including women – whose testimony was not considered reliable in court, so why say it unless it was true – including his brothers – who at this appearance were converted from doubters to believers who would lay down their life for that belief – and then the Apostle Paul – who was converted from not only doubter but zealous persecutor to one willing to die for what he'd seen. Thus, the evidence really is astounding and solid and so must cause anyone willing to listen to think and really ask what this means if it is true (because it is). Blessed Easter to you all,