In your police example, one's disagreement with the law in no way gives them the right to disobey it. By being a citizen of a country, you are entering into a social contract with the government. By staying in a country, you are agreeing to pay taxes, obey the law, respect authority, etc. Your own subjective disagreement doesn't mean a thing. You are free, however, to work to change the law, but this must be done in a certain way. Protests don't nearly do the trick. You need lawyers/lobbyists.
In your robber example, the victims of the murders are still victims of murder. You could argue that they made a stupid decision in risking their lives, but there is nothing immoral about it. All blame rests solely on the one who pulled the trigger, just as with CH. The best you could do is argue that the cartoonists made a poor decision. All immorality rests in the hands of those who killed unjustifiably in cold blood.
In other words, how does the stupidity of the bank robbery victims effect the moral culpability of the murderers?