Regarding the Treyvon case:
Why are killings by police not receiving such attention? Why do everyday street shootings not receive such attention?
Because this case involves a "private cop" or "vigilante" or "armed citizen," who failed.
Police do not like competition. Zimmerman serves to fulfill their prophecies, and is a perfect poster child for gun control and citizen helplessness.
They have created this poster child by making it so dangerous and unpopular for anyone to even think about protecting themselves and others, that only wacko zealots like Zimmerman emerge in such positions. They have effectively trained the population to be both helpless and INCOMPETENT, so that they can say, "See? I told you so," and create a public dependency upon themselves. They even helped nurture this poster child.