It probably won't come as a surprise that being a police officer is a hard job. Consider that, if you see a murder, find a dead body, or counsel a rape victim, this is probably going to be a significant event in your life, one whose consequences you'll be working through for years to come. For a police officer, it's Thursday. And (as with soldiers), police officers rarely get the sort of support that they need to deal with this; there's a culture which really discourages people from seeking out help, thinking of it as a kind of weakness, of not being up to the job.
The challenges of being a police officer are tremendous, and I suspect that the large majority of all the cases where police officers have done serious wrong in the line of duty actually come down to this: dealing with impossible stresses and impossible risks, day after day, the odds of making a serious mistake continue to creep up, and the odds of starting to take the wrong kinds of shortcuts -- especially when there's no real way around them -- start to go through the roof. I don't think it's a coincidence that the worst abuses tend to happen in the roughest precincts.
If we want our police officers to uphold the highest standards of our society -- to do the things that most of them wanted to do when they first signed up -- then one of the most helpful things we can do may well be to make sure that they have the support they need to stay focused, and stay human, despite the things they have to deal with every day.
I don't know what the best way is to achieve this, but I think it's something we could solve, and could be something very much worth solving.