You can buy off US cop's with cash or threats of violence etc. The solution in the US has been the state cops and the FBI, which rotates people around enough so bribing them is less useful. Now add in an internal affairs office with some real teeth. Which creates a structure where bribed local cops tend to only ignore a subset of crimes.

In other words have overlapping independent organizations all investigating each other and add in people that don't stay in an area long enough to be bribed safely.