I've half written my answer to this thread five times now, and I've scrapped and revised it once I think of something new.
Currently I'm despairing over the vagueness of language over morality. To say 'X is evil' is to give X the property of evlness, as seperate and distinct from goodness, then I remembered that Good and Evil are also nouns, and I had a
Wittgensteinian breakdown.
At the moment I am inclined to agree with philosophers like Russel and Wittgenstein in saying that the terms Good and Evil are nonsensical in an abstract non-moral definition, they only make sense once they are linked to situations.
So, raping a child is evil, there is no 'Satan particle/gene/person/neural state' that makes the act evil, just that the act itself is arbitarily evil.