Serino indicates a theory including two face to face confrontations, minutes apart. One at Zimmerman's car (I wonder if that's the one with no words, where Martin gets close, stares, puts his hands in his waistband, then turns and runs), the other at the location where the fight started.
It's more than a theory, I'd say. This is on the recording of Zimmerman's call to police, and there's no reason to think Zimmerman was fabricating this account - although I'm not sure I'd call it a "confrontation": "Something’s wrong with him. Ayup, he's coming to check me out. He's got something in his hands, I don't know what his deal is."
the other at the location where the fight started.
Well, we know this happened. We just don't know how it happened. But there is no known evidence to contradict Zimmerman's claims. Has the Serino affidavit been published anyplace? From the reports I've seen, it's not clear to me that there is anything unusual about it.