Moral responsibility - how does that help anything? Surely it's better to bring those actually responsible - in this case - bombers - via due process, to book?
As for our politicians/ps - I'd expect them to keep a cool head while the mob loses theirs, and be prepared to defend their positions. If it then transpires that they had a part to play in the carnage, I'd expect them to go. This way, we know exactly what when wrong, and the right people have been held accountable.