Given that, oh, not less than 90% of black-on-black crime is gang or drug trade related, that is to say, criminals who have opted for a life of criminality killing fellow criminals who have opted for a life of criminality, I'd say there is good reason for the difference. There is some implied/informed consent to being killed ala "living by the sword", when one opts for the criminal life = occupational hazard = informed consent to the risks.
Not that I think Trayvon Martin was some kind of "victim". He was just following in those footsteps that is so glamorized among his race and culture (emulating thugslife yo, wit mah gold toofs). But since he did not yet have a lengthy arrest record and multiple convictions, its easy to portray him as not yet a criminal. Hey, you gotta start somewhere, right?
Compare and contrast:
"Hey man, what are you gonna do today?'
"I'm going to jump out of an airplane with a parachute."
"What? You know you could, like, die doing that?"
"Yeah, well, you know...."
To this:
"Hey awesome dude, what you doing today?"
"I be dealing some drugs. Representin, and shit, wit mah gold toofs and mah piece. Like a gangsta do."
"What? You know you could, like, die doing that?"
"Yeah, well, you knows..."
Nobody freaks-out over skydivers and base jumpers dying, either. It's informed consent.