If you can't know that Lincoln was shot and killed, you really can't know much of anything in history. It could all be a big lie, maybe for political reasons.
And why do you think proving something scientifically is the only real proof? Can you prove THAT by science? If not, then that claim itself is self-refuting and therefore false.
There is decent scientific proof relating to these matters anyway, but no point in going into that. I'm referring to the Shroud of Turin, which scientists have examined thoroughly, and they have not been able to scientifically debunk the miraculous claims about it.