You would be able to see each night of rioting who returned from the night before because of their literal "glowie" glow. If then the riot police concentrate on the people with the "oldest glow" it would easily id the radical ones and the leaders. If every night their leadership or radical rioters were arrested it would have very big effect on the thing as a whole if done every night. Rather than relying on seeing a face etc, a cop could mark certain people to be id'd later....for example if you wanted to ID an actual individual, you can hit him with any combination of colors....Green, Blue, Blue = Bob where Blue Blue Green = Jane, etc.