He would not get away with it in Beis Din, albeit there are no eidim, and hasra’ah. See M’ Sanhedrin for details. It is very possible that he will be tried in TN,AR, or FL if they find his involvement in additional murders.
As far as the comment that it is borderline kfira to obsess on this. I don’t agree. Obsessing is never good. And Teshuva and limud torah are excellent recommendations. If this was a bear or a wolf or some other wild animal,I would agree. But this is not the case. It’s a person who was given Bechirah who did this. And as much as we recognize that if hashem did not want this to happen he would have prevented it and there is hashgacha in the world, we also recognize that we are faced with a very evil person in our midst and we need to rid ourselves of him.