A reporter is at an all-night outdoor music festival in a city, with reasonable equipment. He is expecting crowds, bad footing, bad light and long distance to the motives, and is carrying a good professional camera for this. (Not a digital camera, more from the "just before digital" age). It is fully dark, and overcast. He is on a kind of balcony overlooking the scene when he notices trouble brewing in a side street below, illuminated only by street lights (the yellow/orange-ish kind): a large gang preparing to stage a riot -- wearing gang colours, preparing weapons, shaking hands with a corrupt policeman, drinking beer, drifting into the crowds, and then all hell breaks lose. The reporter has the high ground, clear line of sight, distance is maybe two hundred metres (I can vary that), and he must not be noticed.
Does he have any chance of getting pictures which can prove later that the riot didn't break out spontaneously but was staged by a gang?
What kind of equimpment would he have, especially what would it look like? (The narrator does not know much about photography, but has good observational skill and is on the same balcony.)
What are the important points to make it more likely that the pictures might be useful? Skill, equipment, anything else?
I had to make a major plot point out of a thing I know nothing about...
ETA: The opinions about what is possible, especially at 200 m (650 ft) diverge a lot. Let's say I reduce the distance to 100 m (50m?) and/or the lighting from "night" to "after sunset"? I want it to be difficult (grainy black-and-white, individual faces not recognizable and fancy darkroom work are fine) but not freaky or impossible without magic.