How is it, that the guns land right in the hands of the people willing to use them? How are those guns floating around, carefully concealed, from purchase to grudge match? How does the grudge match start? Who snitches about what at all?
Clearly someone got shot, and no one knows who did it. No one knows anything? No one knows what happened. Based on that line of reasoning, maybe it's safe to conclude that no one got shot at all.
Except someone did get shot. And whoever did it managed to sail right through all of the gaps you've outlined, and disappear. How did that happen? Who would be motivated to operate against someone disrespecting them in a convenience store argument?
Why taunt anybody in a convenience store? Much less about authenticity or being a tattle tale.
Would you shoot someone for getting snarky with you? A random person at a deli?
If you were the kind of person who roamed the streets with a gun, you'd have your eyes in front of you about getting picked up with it. Even getting caught with a gun inside NYC city limits is a serious thing.
So to carry one around, to know where it is represents a degree of premeditation. Were the victim and the assailant just strangers? The assailant was so chaotic that this is a senseless crime against a stranger during some seconds-long encounter, and yet all so careful, that no one can figure out who dunnit, no one knows how the gun showed up, or why the sudden outburst?
Platonic ideals are great, but hang around some of these delis some time. See what it's like to mingle.