There's no double standard. White people like myself weren't oppressed for generations upon generations, therefore when a white kid is murdered it's natural that issues of race will not factor into the media narrative. It's just the way it is.
All of these random "white person murdered" cases that people like to bring up are an attempt to argue that the media is biased in some way. Yes, they are, in other circumstances. In this circumstance, they're merely jumping all over a story that's ripe for controversy. An open and shut case like the one you mentioned has no long-lasting narrative to maintain viewer interest. The perpetrators were caught.
In the Zimmerman case, the guy murdered a young kid and was allowed to walk free without much questioning. Thus, shit hit the fan. It's not really that difficult to comprehend the differences here.