I would be somewhat suspect of the story the survivors gave, to a degree, and only to play devil's advocate. If you think about it, when someone in
the group got murdered, it would be natural to possibly leave out some minor pieces of information to maximize the guilt on the robber. "We did
nothing, the robber did everything." Max payback against the offender of this heinous crime.
And one that I don't believe has been mentioned yet in here is that once the woman gave the purse up, I have a hunch that the robber may have asked
the man for his wallet, too. Upon which he either hesitated or refused. And at that point, having already been at the scene long enough, and being mr
badass, right before taking off decided "oh, so ya wanna play tough eh?," and bang bang.
Or the man also could have replied "I don't have any money, or I left my wallet at home." Something that robbers don't take too kindly, and who
will often at least smack you hard for. You're supposed to always carry mugger money, so they say. "Oh, so this guy wants to be a smart ass." Bang
bang.
But that may have been left out, and turned into "unprovoked." And I can't say I blame them, but it does change how the story could be viewed,
especially at a conspiracy site.
Until there is further evidence, I don't see a conspiracy here.

