First, after reading all of this thread, (all 18 pages so far), thanks triforcharity and crimreasearch for what you've provided. It's helpful when you're trying to get to the root of it. There's a lot I didn't know.
After listening to Zimmerman's call, one thing came to mind: His work was done at about the one minute mark. He'd made his report, he needed to go home. He had no business trying to be the police officer he wasn't. That he made the call to a non-emergency number indicated he had no information, and further indicated there was no immediate danger to his mind. (911 is for life-threatening emergencies.)
He was told around the two minute mark they didn't need him to follow Martin. By then, there was absolutely no reason to my mind that he should have been out there. He should have turned the car around and gone home. He was done.
Reading the additional links provided suggests this guy has a real racist streak to him, though this is not something I can prove. Nor is there any evidence of his parents holding the positions that Zimmerman claims, (yet.) (Admittedly, there's probably something I've missed.) Regardless, it bears repeating: Zimmerman was told he was done by the dispatcher. He needed to break off his tailing of Martin and leave.
This takes us to the SPD, and what triforcharity has noted: Why wasn't Zimmerman held and at least drug tested? (Background: As a commercial driver, if I so much as put a ding in some guy's bumper, I can be held for a urinalysis.) Following the links, this would appear to be standard operating procedure, yet the SPD violated their own policy in this instance. One wonders why, since this would be one instance when you would demand to know what the hell was going on with the shooter, particularly since the victim was a minor, his race be damned. That there appears to be a pattern of selective enforcement makes me question whether a grand jury or even an FBI investigation will uncover much, since the very people they'll be questioning will be unlikely to provide satisfactory or even truthful answers. (I may be jumping to a conclusion here, and I hope I'm wrong.)
What we actually know is disturbing enough. I'm almost afraid to hear more. I doubt it has as much to do with race as much as it does procedural laziness.
There's something else, too: As Darth Rotor pointed out, after 18 pages, there are certain posters I respected who look very foolish. I'm hoping this is a misunderstanding on my part.