Terrorism by Model Airplane in Germany?

There are some amazing airplane and airport models out there:

On a darker note, however, there is developing news as German authorities are investigating two men of Tunisian origin suspected of planning to use model airplanes for terrorist attacks.  Police in Germany and Belgium raided a series of sites searching for evidence of “possible attack plans and preparations.”

As the story develops, there does exist a relationship between model airplanes and unmanned aerial vehicles.  Specifically, some of the first guidance ever offered by the Federal Aviation Administration (“FAA”) was in the form of an Advisory Circular (“AC”) establishing operation standards for model aircraft.  Among other things, the AC prohibits operation above 400 feet.

It is curious, and frustrating for law enforcement, that under current regulations and guidance authority, the FAA will allow model airplane operations up to 400 feet, but “drone” operation in that domestic airspace is being stamped out by state and federal legislation.  Why the difference in treatment?  Presumably the surveillance capabilities of drones versus models or “toys.”