I don't think it's a problem of the police but a politics problem.
The politicians are the ones who create the laws that give too much power to the police (or take away power from the people).
Killing people is never a good way of solving problems, specially when the ones that are killed are just a small part of a large organisation.
Do you kill some cops to try to get even? The politicians will created new laws to take away even more people's rights or to give more power to the
police. Remember, the police never ends, they can always get some more, and the bigger the power they have the more we will see people on police
forces that joined exactly because of the power they will gain over the common citizens.
Here in Portugal something like that would never happen, do you know why? Because nobody can enter someone's house without being let in or without
showing a warrant. After sunset and before sunrise, not even with a warrant can the police enter someone's house without being let in.
This was one of first things changed after the revolution that ended the 48 years dictatorship in Portugal, before that the police could enter
someone's house when they wanted, day or night, and it was common to be wakened in the middle of the night by the police (or the political police) to
be taken to jail just because someone had told the authorities that you had some "subversive" books, for example.
The change of mentality after the revolution (the
Carnation Revolution) saw an obvious
change of the laws, and the change of the laws resulted in a change of the mentality of the people who entered police forces, from the mostly
under-educated people that saw it as a good way of having a better life than common people (because of the power the regime gave them) the police
turned into a force of people that (mostly) wanted to help other people and to help his country to become a peaceful place.
So, after this unusually long post, and in conclusion, I think that the "cure" for this problem is in the politics that create the conditions for
this to happen; change the politics (and you have the power to do it, we did not had that power until 1974) and you can (and will) change the
direction your country is going to.
Remember, it's always easier to enter a dictatorship than to end it, don't let it start!