Lewis Thornton Powell

I have been reading Alias "Paine"  by Betty Ownsbey. It is about one of the men who conspired to kill President Lincoln.  From what I have read, he started out a gentle, kind person. So what caused such a man to become an assassin and attempted murderer?  Once again it makes me ponder what atrocities will a person perform when they feel they are morally justified?

Here is a picture of Lewis Powell