That is a possible explanation. In the US the FBI's investigative powers supercedes that of the local police, and they are centrally managed from Washington DC with satellite offices in the various cities around the country. They are chartered with investigations that would cross state boundaries typically and are the investigative arm of the Department of Justice. The Russians and Canadians have similar services (examples of 'large countries') as does China.

I meant large in terms of people. It's hard to keep tabs of remote areas, but even harder to keep track of large groups of folks. This is why China's the best example.