Some of these guys won’t have any compassion no matter what you do. I remember reading a study where a psychologist concluded that anyone who wanted to be a police officer should be prohibited from being a police officer because they were overwhelmingly shown to be people with control issues. Not that all police are sociopaths, but after years of seeing their behavior in New Orleans after Katrina and of a few years of seeing how “Shoot the dog!” is an official cop pastime it is quite clear that too many cops are, indeed, sociopaths.
Earlier in my career I spent a number of years doing comprehensive psychological evaluations of applicants to local police forces. Your statement is false, and I challenge whether any such "study" ever existed. Lots of psychologists are liberal morons, to be sure, and may hold that private opinion, but there is no study characterizing police officers this way.
Are there bad cops? Of course. We sometimes rendered a "do not hire" recommendation to our departments. They universally followed this guidance in the small number of cases where it was indicated. So what happened to these psychological rejects? They got jobs with departments that didn't bother using serious psychological evaluations.