A sociologist became a cop in Baltimore's Eastern District and lived to write about it. It's a good book, whether you're looking for some background on The Wire or just want some reminders about why policing is basically impossible. Are you keeping the peace or enforcing the law? When you signed up for the job, did you really understand just how much carefully-phrased documentation you'd have to write to convince folks that an arrest was justified? When you imagined tackling bad guys, did you assume that they would have showered within the past few days? The futility of chasing drug dealers off a corner (for five minutes until they reconvene after you've been called off to some other spot). How 911 came to be a joke.
A good book to read when potential police trigger-happiness is on peoples' minds. Sometimes it's bad police. Sometimes it's reasonable police in a bad situation. Sometimes it's: Why is that city trying to solve this problem by means of armed guards when if you thought about it for 10 seconds you realize that would never work?!?