A lot larger as in landmass. People pay attention to what goes on in their geographic area, regardless of its population.
For example, a beating in California isn't going to be as troubling to a resident in Vermont. They'll simply say "different state, different police force". On the other hand, a beating in Berlin is going to trouble someone in any part of Germany.
Not true: the former border police (Bundesgrenzschutz, parent organization to the famous GSG 9) has been officially the Bundespolizeit (federal police) since 2005, and there has always (well, since the 1951) been a federal investigation agency (Bundeskriminalamt). Most claims of police violence are actually against the Bereitschaftspolizei (riot police units, exist both at state and federal level), which is not surprising since they are deployed (and trained) mainly for potentially violent situations.
To clarify: I know there are federal investigative police (but not as powerful as the FBI, right?) so I deliberately used the verb, meaning enforcement. I didn't know there were federal riot police though.
ANYWHERE you get people whose jobs are power-over-others based, you'll get fuckwads taking those jobs to feel powerful. Then abusing those jobs for the same reason. It has nothing to do with the nation and everything to do with the nature of people and policework.