As I am from the UK I don't feel that I can't fully comment too much on the situation in the US, but the situation we have in the UK points to the fact that on both sides of the Atlantic, there has been a growing underclass of bad cops, somehow avoiding the very system that sets standards and have been allowed to commit all sort of crimes with complete impunity.
The US has been beset by racism for a long long time ( we know that), so it is almost engrained in to the system. Watching a programme call called 'Dom digs in' ( https://www.bbc.co.uk/programmes/m000vl0v ), where cameras follow Dominic Littlewood (TV presenter) in various jobs, he did team up with some police officers in the US for one such programme, what strikes me is that every job the police are called to, they are treating it as if it will result in a gun battle, so they are already on a heightened state of alert, fully armed, vests, shields etc even for something that seems trivial.
There is NO excuse for the way the police behave, The police are not supposed to be a paramilitary force, I get the impression in the US they seem to have become that. Both sides of the Atlantic, the police have lost the trust and respect of the public, to the point rather than the police being a point of contact for any concerns, people are fearful of even approaching an office. This is just not healthy anywhere.
Of course the US, everyone has the right to bare arms, so anyone can carry gums from small side arms to what seems to be fully automatic assault rifles etc.
Both side of the atlantic need to re-think policing, get back to recruiting people suitable for the job, robust screening and make it very easy to kick out who breaks strict rules of contact, as Trump once said 'Drain the swamp' perhaps in the case of policing he was actually right. Decide what the job of policing should be and have proper scrutiny and accountability of all officers regardless of rank.
Of course this needs to come from the top, perhaps a few properly worded executive orders from the president can start to change how the police operate,