International Police Force, border jurisdiction on Bush's Flight marshalls

I think the idea of armed flight marshalls is a bit of a non-starter for pretty muchthe same reasons that have been outlined in the "SHould Pilots Be Armed" thread. And I can certainly see them getting antsy if a Middle-Eastern passanger even twitches or goes for his hand luggage mid-flight. Nevertheless it throws up an interesting sideline.

On internal flights they are fine, they can be authorised and policed by the country they are flying in. But which worldwide body would control and run this airborne police force on international flights. Presumably if the destination country does not want armed police of another nation on their soil, so how could this be smoothed over? Or think of your own nightmare scenario of one going crazy apeshit bonkers and being the only fella on the plane with a gun...