It's hard to convince somebody to change his ways when he has been doing it wrong for decades, and all his peers say it is the only way to do it. And in every police force or military are real jail material who gets there only to beat people for joy.
New generations should be easier, but probably will get contaminated by veterans.
But you can't get good professionals without good training.
Having a good training is not going to solve it, but I think is unavoidable to do so.
Maybe they have to end up resetting all of police. And have gun control laws that aren't a joke. And many other things.