To make this point worthwhile, you need to start evaluating the claimed and possible reasons for the decision. Decisions like this are routine in police work. Perps like Josh Powell walk from custody when it looks like there isn't enough evidence to make the arrest. That's what upline officers are supposed to look at, and that's how the decision should be made.
It's probably routine for the cops on the beat to want to make the arrest and push for results from their work, and probably also frequently true that they haven't got enough evidence.
What will be crucial in this case is not the testimony of friends and neighbors, which perhaps the upline officers didn't know about at the time the decision to release was made, but which should have been sought at the scene. The officers at the scene have the duty to report/testify and should have dealt with, and reported the injuries, if any. And that is what the upline officers/authorities should have considered in making the decision to release. It will be, for purposes of making a case of favoritism, crucial to evaluate the integrity of that primary evidence.
Salty, it's just not credible for you to diss the friends and neighbor folks who said they saw Zimmerman the next day with a totally idiotic and irrelevant objection that they weren't eyewitness to the "incident" itself.