My concern would be a small drone like Children play with seeming innocent but carrying a hand grenade in a city

So, after reading and seeing a few videos you could see that ISIS might deploy small drones with hand grenades over a city anywhere in Europe or the U.S. People wouldn't suspect anything because small drones used by children and adult enthusiasts are everywhere now so no one would even think about it. But, what if one or several were deployed in a city dropping bombs and hand grenades on innocent people all over the place. This is my concern as I see videos from Mosul, Iraq these days.

There might be no terrorists to capture because you might not find the operators either for a variety of reasons. So, this would be a crime you might not find the terrorists behind it either until it was too late to find them. You could trace where the drone was from (if it was shot down). You could trace where the weapon was manufactured that was dropped (from it's fragments) but you might not find the terrorists behind this because often they steal the drones in the first place and then modify them. So there would be no buyer research because it was stolen in the first place. and the hand grenades might have been stolen too or manufactured or assembled at home or in a garage somewhere.