The problem is that they are dramatically limited in the types of charges they can press against officers of the law (charges that carry big penalties, and have a very high burden of proof). This is anachronistically because we as a society have decided that officers deserve benefit of the doubt in the lack of compelling evidence. These days, many instances of misconduct are recorded, and the rules should change.
In Eric Garner's case, for example, the govt attorneys declined to press charges, because they lacked sufficient evidence that the officer was knowingly violating the rights of Eric Garner. The burden of proof for any kind of misconduct charge is currently so high, that even an egregious misconduct case like this passes by untouched.
If the attorneys general had a wider range of misconduct charges in their arsenal, they could raise the average cost of police misconduct, and it might improve the situation.
[1] recently informed by https://www.stitcher.com/podcast/pushkin-industries/deep-bac...
This is where the department of justice, and state-level attorneys general should be able to check and balance the system, but current laws render them unable to do so effectively.
Even during the Obama years (Eric Garner happened while Obama was POTUS), when a DoJ that wanted to do the right the thing was empowered to, these laws were a huge impediment to progress.