Can Christians be police officers?

I think that to begin with this question, before addressing the larger question of, "Are Christians to take part in war, violence and killing others?" is to put the cart before the horse. I don't believe that the place to start when determining what one believes about God is, "is it okay for me to do/be such-and-such?" My ability or inability to be a police officer should not determine what I believe about God or what He says. I am afraid that an answer to this question, before it is determined what the role of the Christian and the State and the Christian and violence are, would keep us from addressing the larger question of what and who Christ has called the church to be.