I think there has always been police brutality and abuse of power - but limited to the "lower classes" of people.
I also think, though, the militarization of the police has been disasterous - and there has been a real shift in police attitudes from what I can figure. For example, now the attitude is that a police officer should never take the slightest personal risk, not just hit or shoot fast - but also just in rescues.
There was a disturbing story about a woman taken hostage in Dallas and a police SWAT team showed up outside the Apartment. It known to the SWAT team this the situation entirely. Soon they heard two shots. The woman then shouting that he shot her and then shot himself in the head - pleading for help.
Even though the SWAT team wearing full body armor, knowing it certain the man only had a handgun, having heard the man stop talking and the shots and then instead the woman saying what happened, they absolutely refused to go it, telling the woman she had to open the door and come out - to her saying she was shot and couldn't. The SWAT team absolutely would not go in for her. I think that represents a change of attitude. Yes, some scenario could be thought of for danger going it, a 1 in 100,000 scenario. In short, that woman/victim was 0% and the SWAT officers 100% in value in current typical police policy.
There are clear dividing lines increasingly between "us police" and "them people." I think the extreme military gear, the training for mass civil conflicts and terrorism even in small communities where such never has and likely never will happen, and the training in psychological domination and self-protection at-all-costs, plus how the political structure works is degrading the psychology of police officers in may departments.
So I think abuse and brutality have always been there, but that attitudes are changing for the worse. For so many reasons, I tend to think on average police care less about people than they used to.