... yet will deny any responsibility when their insanity blows up in their face ...
Worse than denying any responsibility, they deny it happened. I don't mean the event itself, although they would if they could -- look at how few Black on White crimes actually make it into the mainstream news -- but even before the facts are established, they're already denying terrorism (lone wolf) or that islam has anything to do with it.
For all the words there are for lying, I can't think of one that describes the malicious evil of these type of lies.