"Law enforcement" is not empowered to enforce FAA regulations. Besides, if the footage were being given as evidence, it can be edited to show only a short clip. The location of the operator is not included in the footage, so it would be speculative at best as to whether the operator could see the drone at the time of recording. It is very difficult to prove in court, so enforcement is kinda limited to charging folks when their drone has been captured or crashed where it was not permitted.
Of course, anybody in law enforcement could pass along the video to the FAA, but that doesn't seem to be the sort of thing that gets their attention. They are much more concerned about drones intruding into forbidden airspace. If you were caught flying your drone in a quick flight over the White House, you might get put in jail for a while. The entire DC area is banned for drones, as is any area near an airport or over a federal monument.
Curiously, National Parks are not off limits at all, but you cannot operate a drone from within the park's boundaries. You see, the National Park Service knows that they have no authority over the sky overhead, but they damn sure can regulate what you do when you are on the ground. So a drone flying over the Grand Prismatic hot spring at Yellowstone will get a really serious penalty for the operator, should they be able to catch them. They also have a pretty rigid attitude about issuing special permits for filmmakers.
Once the operators log is captured by the FAA, they have an easy case, however. It reveals altitudes, and the GPS log of the drone and the operator's location. At that point, it becomes a slam-dunk. But they don't get involved with that level of investigation until the operator is already in trouble for something else.