Well actually that brings up an interesting piece about how the US is structured. I think the reason your police can be more corrupt is because of the federated nature of policing.

Cops are usually only answerable to the mayor of the city (and sometimes the electorate) rather than higher ups in the government. So there is a lack of authority and control there. If they were answerable to politicians and politicians were actually responsible for their actions you could take very firm political actions against those politicians - but in the states nobody in the Cabinet or Government is responsible for law enforcement.

And I understand why this federated system was originally put in place, but this isn't the 1700s. In communication terms the US might as well be Iceland - you can communicate from one end of the land mass to the other instantly, so we don't need to have localized and federated decision making.