It's not just the "black community" that's angry, trust me.
It's every parent in the United States who has an empathetic bone in their body.
You don't have to be black to imagine what it would feel like if your teenage boy walked to the neighborhood convenience store for Skittles and a can of ice tea, and never came home again. You don't have to be black to imagine what it would feel like to know that your baby died trying to get home to you, that he was frightened before he died, and that the individual who killed him is the very one entrusted by the community to ensure the safety of all of its residents. You do not have to be black to imagine what it would feel like, then, if this individual was not even arrested.
It would be worse if you were black, and if the killer in question was heard muttering racist epithets on the 911 tape while pursuing your child... but it's bad enough even if you're white.