The police want to trap him. There is a rule developing that under no circumstances should one shoot a black; even if he assaults you, attempts to rape your wife or daughter; beat your aged father to death; fire a shot at you personally etc. etc.
They have to at least make a token request, for appearance sake.
If the shooter can't identified, he or she would make grave error to report to the law. There is no benefit, only downside risk. Not only downside risk from the cops, DA and judge, but also from the dead hoodlum's friends.
I guess you have to make sure you’re the only witness.