If the Jews or Romans had produced the body of Jesus, Christianity would have been immediately disproved.
This has always struck me as a very weak argument.
I don’t think that the Roman practice was to prove to troublemakers that their beliefs were incorrect. Rather, the Roman practice was to prove that their beliefs were ill advised. They did this by hanging a bunch of them on crosses, sacking a town or two, and shipping a couple of boatloads off into slavery. If Paul is any example, the Jewish authorities weren’t much into persuasion either.