"That is so untrue! I suppose you can attest to this beyond a shadow of a doubt? "
Prove me wrong.
"It has been said that there is no such thing as a perfect murder."
I think O.J. proved that one wrong, didn't he ?
I bet you were on OJ's side as well.
I actually think you have to prove the veracity of your statement also, not belabor those that question it. For them to prove you wrong, we need to know what you are basing that assertion on.
You are right about OJ.