Evil Serial Killers

Saturday at Barnes & Noble on the bargain table I saw a book called "Evil Serial Killers," and thought, "as opposed to all those good serial killers out there?"  The only supposedly good one is Dexter, a fictional character on HBO.  Is the author making a distinction between evil killers and mentally ill killers?  Couldn't a case be made that all serial killers are both evil and mentally ill?  Maybe evil and crazy are the same thing.  Nevertheless the word "evil" in that book title is seriously redundant.