Nobody is claiming that Trayvon Martin or this teen deserved to die. As far as Treyvon's case, his life was not threatened just because a man was following him. Both parties acted irresponsibly that night, and placing the blame squarely on George Zimmerman or Treyvon is silly at best.
Regardless, what happened that night has very little to do with what happened this time. The facts are still coming out as the investigation continues. This "guilty until proven innocent" idea is getting a little out of hand. Not just in this case, but everywhere. It's getting quite worrying and quite annoying to see.