neighbor: "groups of young men (teenage/late 20s), dressed in masks, black commando outfits, carrying M16 rifles, running through the neighborhood"

See this 07-09-2017 message from a 2nd Street NW neighbor:

Has anyone else observed this? I just wrote the following email to my ANC Commissioner, and the constituent relations managers of my City Councilperson. Any advice would be welcomed: I'm writing because in the last week, a deeply disturbing activity has surfaced in my neighborhood. I have witnessed, at least a half dozen times, groups of young men (teenage/late 20s), dressed in masks, black commando outfits, carrying M16 rifles, running through the neighborhood at top speed, both day and night.
                        
The first time I saw this, I almost had a heart attack. It turns out, they're playing paintball (although no paint evidence is left behind - so I'm not quite sure what the substance is). They are running through the neighborhood, terrifying drivers, pedestrians and residents.
                                                   
Lastly, these young men are all African American, which, in light of Tamir Rice, and the list of other black men who have been killed, leaves me terrified that this is all going to end very badly. I don't really known what to do, since they are not real guns. 
                                  
Nevertheless, perhaps this kind of activity is illegal, and at the very least, an exercise in unbelievably, exceptionally poor judgement.
                                                    
Do you have any thoughts or advice on the matter?