TH, I see your point - I really do.
Unfortunately, you are focusing on the wrong aspect of comparisons about this case, the Zimmerman case, or even the Marley Lion case.
The reason the Zimmerman case is national news is because there was no clear answer (regardless of whatever your personal beliefs may be, this is an undeniable fact). Some people adamantly say he was guilty others say he was not guilty. Some say he was a victim, others say he was a murderer.
This case you posted is about horrendous street crime - as was the Marley Lion case. In both instances, the GENERAL PUBLIC can clearly see that "criminals shot an innocent victim" and should be punished thusly. In the Zimmerman case, this comparison cannot be made.
Sadly, street crime is so prevalent and so ingrained into our society that stories of no constroversy but merely street crime are not news worth enough to go beyond local news.