The missing factor in Zimmerman's case, or at least publicly missing, is the training and instructions given as a leader in the local Neighborhood Watch. This training is given by local law enforcement, and it puts things into a different category when it comes to his following rather than just reporting. I'm sure this will be a part of the defense.
In the NW groups I've had any interaction with, the "instructions and training" was:
These are your neighbors, try to get to know them - at least by sight.
Look out for one another, call 911 if you see anything suspicious.
The only thing that PD did was bring a cop car or K9 unit to help with the dog & pony show. That's where I came in - "Hi kids, wanna climb on the firetruck?"
The "Leader" was the guy who wanted the NW in the first place and made some phone calls to get the cop car/firetruck to said dog & pony show.
Oh, we also passed out some phone stickers that you could write you address on (not a bad idea since the babysitter may not know your address) and it had a big red 911 on it in case you forgot the number.
Might be different in some locales but this really wasn't
training. The 911 operators
are trained to ask the questions in their queue and be able to type that info while asking more questions.