"can't just cry 'gang' and close the case."


Oh really?


From the story you linked to:
Last week, Detective Superintendent Gordon Allison, of Operation Trident, said the boy whose funeral it was had "contact with gang members".
But he added that police were keeping "a very open mind" about the motive for the attack.


Just because the guy who was shot was the wrong guy, doesn't mean it isn't gang-related activity. Just as it doesn't mean it definitely was gang-related either.