It's ot up to the Prime Minister, or anyone else, to tell people how they should feel about something. It's not up to him to tell us who we should, or shouldn't, feel sympathy for.
Do I feel a huge amount of sympathy for Raoul Moat? No. Do I feel a small amount, as I would feel for any other human being who was clearly deeply unhappy? Yes. Do I feel more for his victims and their families? Absolutely. Do I expect everyone else to share my feelings? Hell, no!
If David Cameron wants to announce that he feels no sympathy for Raoul Moat then that's his choice. But he shouldn't claim to speak for me, and he sure as hell shouldn't be telling me what I should feel.