there has been many cases in which police have killed innocent people however found not guilty for it, why
because unless its a very serious offense, its generally better for society to let the police off. Think about what would happen if you didn't.. your going to put police in dangerous situations, where the whole time they are worrying about whether they will be the ones who end up in jail? They will be scared, timid etc.. to afraid to do anything, in case it backfires on them. That's not the sort of police force you want.
So you need to give them a bit of flexibility, so that you have a police force that is confident enough to act, and to step into risky and dangerous situations, knowing that largely the state has their back if things go accidentally wrong.
Obviously this will lead to some cases of miss-justice, but overall those will be outweighed heavily by the net positive effect this confidence has on the police force.
(BLM presents a similar problem. You now have American police who are afraid of stopping and confronting black people, and are not following their usual trained habits, because they are so scared that if the situation goes badly, they will be public enemy no.1 - on the covers of all the papers, in the news, and over-night become one of the most hated people in America... a functioning police force needs confidence that the people and state are behind it, and that is a far greater positive then the negative of the small-scale corruption that it makes easier)