I live in a crappy neighborhood, and our neighborhood watch does the same thing, and we are coordinated with the sheriff dept. The whole point of the watch is to identify people that don't belong. If I see some suspicious folk walk by my window, I will make my presence known by going out on my porch with phone in hand dialing sheriff dept, and continue to follow their activity to note description and direction of travel.
We have nailed two dealers and break ins have reduced since the watch started. It was reported on my local news today that Zimmerman has called in many reports, so it sounds like that neighborhood has problems too.
There are such folks ~ they aren't all nice guys.
There was some discussion today of OTHER MURDERS that followed this same pattern in that area, so there may be a lot more going on here than we know about at this time.