Okay, I've had a few bourbons, but I'll give it a go. Don't take this as absolute gospel.
It's hard to gauge because only about 850 police departments contribute data to the Uniform Crime Reports System. The only statistic I can think you can look at as a measure of actual police violence against citizens is looking at the "Justifiable Police Homicide" rate (meaning a police shooting wherein no criminal charges were filed against the officer). "Police brutality" is such a broad, subjective term and there's no national statistics on the rate of complaints filed against officers or the amount of time an officer has to use force.
So I'm just going to use the FBI's Justifiable Homicide rate. This is also what high-profile deaths like the shooting of Michael Brown are classified under. Keep in mind, this is only looking at about 850 of the 17,000 police departments in the United States.
Here's a graph showing the FBI's Justifiable Homicide rate from 1991 to 2012.
From 2012 afterwards, the statistics per year were:
- 2012: 426
- 2013: 471
- 2014: 444
There's no data yet for 2015.
One thing to keep in mind as you're looking at these statistics, the number of police departments in the past few years to actually provide data has risen in the recent years under pressure from Eric Holder's Justice Department. There were only about 750 reporting in 2012. In 2013 and 2014, they added about 100 more reporting police departments.
So from this, I think the argument could be made that police brutality (at least in the context of "justifiable homicides" like the death of Michael Brown) has only barely increased or stayed flat. It's just our attention to the issue that has grown. Again, this is only a small sample size of the big picture here.