When exactly was it established that Trayvon Martin was "acting strange"? What's our source for that?

Before Z had done anything for which he could possibly criticised, still sitting in his car, he called the police and said,"Hey we've had some break-ins in my neighborhood, and there's a real suspicious guy, uh, it's Retreat View Circle, um, the best address I can give you is 111 Retreat View Circle. This guy looks like he's up to no good, or he's on drugs or something. It's raining and he's just walking around, looking about."