This case is fucking insane. The guy was found not guilty, which means what he did was reasonable under the law. Which means he did not have some premeditated plan to kill this kid. The FBI has narratives in some of their investigation stating that they interviewed over 20 people who said Zimmerman had never shown any racist tendencies prior to the shooting. But, the DOJ feels the need to investigate to see if this was based on race. Over 300,000 people have signed a petition at moveon.org urging the DOJ to file a civil rights case against Zimmerman.
There was no crime committed, but that's where this country is now. If you don't like that the police aren't charging somebody with a crime that you want them to be charged with, go nuts, raise hell, make petitions until they cave and do what you want. If you don't like the findings of a jury, go nuts, raise hell, and make petitions until they cave and do what you want.