The Trayvon Martin case is an opportunity to remind people of the reality of interracial crime in the United States.
For the purposes of this analysis, I'll use the term "whites" to refer to whites plus Hispanics since they get lumped together in the data. According to FBI data for 2010, 218 blacks were murdered by whites. Blacks murdered 447 whites. But this is comparing apples and oranges since whites are 6.4 times the size of the black population. If we calculate murders per 10 million in the race-specific population (interracial murder is rare), the rate is 8.82 for whites and 114.89 for blacks. So blacks kill whites at a rate 13 times higher than that of whites killing blacks.
Another way to look at it is multiply the black population by 6.4 to make it as large as whites. If it were as large, 2861 whites would have been murdered compared to the 218 blacks killed by whites.