One of the things that bothers me the most about most law enforcement officers, and most prosecutors, and many judges is that they never have any doubts.
They don’t doubt that they’re right, when they’re wrong. They don’t doubt that they already know who did what — who committed what crime, who aided and abetted, who was an accessory after the fact, who is lying, and who might be telling the truth (usually because their story supports the officer, or DA’s, presuppositions) — even when they’ve got the wrong person. And it’s nearly impossible to change their minds by pointing to some piece of reality.
Especially if that piece of reality only comes to light after they’ve made up their minds.