I don't think there should be a trial if there isn't evidence to support that GZ committed a crime.
It isn't a crime to follow someone, to keep an eye on them once you've called LE. It isn't a crime to shoot someone to death who is causing you grievous harm or a reasonable person would think they were about to cause grievous harm or death.
The video in the police station, the clear version of the video, makes the injuries to the back of GZ's head obvious. The witnesses report that Trayvon was on top of George, as the evidence suggests.
You can't take someone to criminal court just because it's sad that a young man has died. A crime, that's reasonably provable, has to have been committed.
This case is appropriate for civil court, where you can seek redress for losses where a crime hasn't occurred.