My reason is simple - on consideration, I believe that we all have equal responsibility to uphold the law. I stated that as a question at first and then repeated it as an opinion. It can't be reduced any further IMO, but then again I tend to favour categorical rather than consequential answers to moral questions (albeit not exclusively).
Just had late lunch with my son and friend who are/have both studying/studied philosophy and ethics. They started the same way. Initial reaction was that the policeman had more responsibility than the average citizen. But within two minutes and a digression into Virtue Ethics and Aristotle, fireman and arson and headline acts at Reading tonight, they both changed their mind to more of the " we all have a responsibility to be moral citizens" belief.
Still an interesting question. And then, assuming guilt on the part of some of the police. Who do you charge? The office wielding the baton, his boss, the government? All three!?!?
(no I don't think that teachers have more responsibility to teach than anyone else. God forbid if that were the case! Our head makes the same point to parents at the start of every year!)