It's not that the police officers were not genuinely good people. In most of these cases, the police officers honestly believe they are doing the right thing and putting a murderer behind bars. The problem is they zeroed in on the wrong suspect. Once they "knew" (incorrectly) who did it, they naturally stopped looking at other possibilities and built their case around the wrong person. That's the situation you see happening again and again in these false conviction cases: Michael Crowe, Timothy Masters, The West Memphis Three, it's the same story over and over good cops who think they are doing a good job and caught the people responsible for a heinous crime but who were flat out wrong.