Syag, Trayvon Martin was in the act of murdering George ZImmerman. He was bashing his head into the concrete. What he looked like had absolutely nothing to do with it. Nor did his race play any role in the entire episode.
And the death of such a person is a good thing, because it makes everyone around him safer. All the people who would have been his victims had he lived are now safe from him. Ba’avod Resha’im Rina. The Gemara says explicitly that although Hashem does not rejoice at the death of the wicked, he encourages others to rejoice. When the Egyptians drowned He didn’t want the mal’achim to sing, but He did want us to sing. Binfol Oyivcha applies only to our fellow Bnei Yisrael.