While I don't know about "official" it was widely known in the community (which perhaps it should be pointed out was a mixed race community) that he was a neighborhood watch volunteer, and indeed a captain in it.
Merely because the prosecution decided to use an emotional argument of "want to be cop" doesn't change the fact that he was part of a legitimate neighborhood watch.
The short answer is that if what he did was part of being a legitimate neighborhood watch then he would have been instructed to do it and how, and identified as someone doing it, with the cooperation and support of the truly legitimate neighborhood watch—commonly called the police. Instead, the real neighborhood watch explicitly told him to cease his illegitimate actions and return to his car. He disobeyed.
As with real police officers in operating in plainclothes, how is any ordinary person supposed to know he's not facing just some random thug when zimmerman* approaches? Eventually cops grasped the danger they were creating by their 'disguises', and now train and equip themselves, because not establishing legitimate authority costs innocent lives.
This guy 'legitimately' interfering with an ordinary person's lawful right to peaceably go about their business, wore no identifying uniform or badges, had received no serious training either in the laws of arrest (stopping people) or tactics (how to do it), or even in what constituted behaviour that should be noted. Further, he deliberately disobeyed what few instructions he had received from the truly legitimate authorities. If he indeed had any legitimate business stalking martin, the authorities didn't think so.
All one can say is that in a highly politicized trial Zimmerman was not convicted of the offences he was charged with under the misbegotten laws of Florida, and must be presumed innocent of them. A far different thing from being not guilty of carrying out a homicide that a trivial exercise of simple common sense could have predicted and avoided. It's why he was instructed to disengage. Carried to that horrific end, it was inarguably criminal stupidity.
I can quite agree that the prosecution followed the police (remember how long it took to charge Zimmerman at all) in bungling the case, and certainly the shenanigans on the bench were no help in arriving at a just and proper result. But who in those parts—apart from the Martins and a few of their friends—had any interest in that, if it meant 'one of ours' being sanctioned?
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*After this result, it's clear the proper and appropriate action when approached/stalked by a zimmerman is to shoot first aiming for centre of body mass. At least in Florida.
