From what I've seen of police misconduct, the general form of misconduct is that the police officers generally just blatantly lie. The problem isn't that they're editing records of things that happened, the problem is that they're lying about the records in the first place--and I think the George Floyd protests make perfectly clear that they are more than willing to lie even when they know that hard evidence (in the form of other people recording the scene) contradicting them will exist.

That's the basic problem with blockchain: it only really provides nonrepudiation (someone can't back away from a statement they made previously). It doesn't have a solution for people willing to commit perjury, and when you look at all of the social situations where official records are distrusted, the main reason for that is that officials are known to be committing perjury and face no repercussions for it.