I think it's not just that Hollywood movies are influencing the Police, although that is part of it. Art both reflects and influences culture. It's hard to separate out causes and effects, although it's clear there is a problem here.
American culture as a whole places a ridiculous emphasis on empowerment through violence. It's everywhere; films, tv, books, music, punditry, news reporting, people's attitudes and idle conversation. A huge proportion of narratives resolve themselves through heroic violence. Often a heroic character will find inner strength through physical violence (and often inner strength means becoming murderously callous).
If you take a step back and look at it critically, it is rather absurd. In the real world true empowerment comes from intelligence and leadership skills. In the real world, having to kill lots of people would be very traumatic (at least for a well adjusted person).
I don't think it's as simple as violent movies causing violence. I think the real dangers come from the unspoken assumptions, the things that movies take for granted, which then become part of everyday thinking.