It's funny you say that, because most of the Zimmerman defenders argue that the media, besides Fox News, was biased against Zimmerman, only showing pictures of Trayvon when he was younger and editing the 911 tapes to make Zimmerman sound more racist.
in fact, Zimmerman sued NBC over that shyt
George Zimmerman sues NBC Universal over edited 911 call - CNN.com
bottom line is that whenever there's a controversial issue, both sides would rather argue the media is biased against their side rather than admit the media has their back. basically, the media can't win in any situation
as for the OP, depends on the context
20 black men killed due to gang violence over the course of a few weeks wouldn't be that big. but 20 black men killed at once by a racist white shooter would be huge. think of Trayvon x10.