Trayvon was loitering in the rain off the sidewalk, near townhomes in a neighborhood that had been burglarized frequently in the recent past. Zimmerman thought he might be high as well.
Zimmerman gave a reasonable response: he called police and tried to keep them abreast of where Trayvon was at.
Trayvon noticed that somebody was watching him. He presumably had no way to know whether it was a “good guy” or a “bad guy”. He hid. A reasonable response.
Zimmerman couldn’t see Trayvon any more. He headed back to his truck. At that point neither Trayvon nor Zimmerman has any reason to pursue things further. The reasonable response would be for both of them to go home, or to make further contact with police regarding what had happened.
Then Trayvon comes around and initiates a conversation with Z by asking why Z is following him - a reasonable action if he wasn’t afraid of Z and wanted to clear up what had just happened. Z responds by asking why Trayvon is in the neighborhood, which is the reason why Z was trying to keep track of him - a reasonable action for somebody who wants to make sure that somebody isn’t “up to no good”.
The problem is that bolded part - from what I've read, we only have Zimmerman's statement as to the accuracy of those events. It is possible that Zimmerman did stop running after Martin when the dispatcher made the suggestion. But there is no independent verification that he returned to his truck, only his statement.
There is also no independent verification that Martin was the one to approach him. The statement by Martin's girlfriend was that Martin SPOKE first. If Martin did duck out of sight and Zimmerman was still walking around trying to catch a glimpse of where he went, it is possible that he rounded a corner and found Martin. In which case it would be very reasonable for Martin to respond with "Why you following me?"
How thing disintegrated into a life and death struggle isn't as open and shut as so many are implying. Based on what I've read of the evidence so far, they don't have anything to verify Zimmerman's version of events but they don't have anything to dispute it either. Unless they've got an ace up their sleeve that hasn't been released to the public yet, this is going to be a very difficult case for them to win.
After looking at the timeline and map at http://floppingaces.net/2012/04/03/the-martinzimmerman-timeline-reader-post/ , it looks like he didn’t get back to his truck but could have been headed that way.
I need to further digest the timeline, but the girlfriend said the phone went dead at 7:16 - which was about 30 seconds after Zimmerman got off the phone. The cops arrived at 7:17 so there was about one minute for Zimmerman to receive the wounds he received and shoot Zimmerman. 40 seconds of that minute included someone screaming - during which time 911 was called. There’s some wiggle room for rounding on the minutes, but that’s not much time for any kind of chit-chat. If the scream was a desperate scream for help it probably came after the broken nose. So within 20 seconds or so Zimmerman went from answering Trayvon’s question with his own question of “What are you doing in this neighborhood?” to having a broken nose and screaming for his life. Sometime during the 40 seconds of screaming Zimmerman apparently struggled his way off of the sidewalk and onto the grass.
Or if a person doesn’t believe that it was Zimmerman screaming, then within 20 seconds Z attacked Trayvon, Trayvon responded by breaking Z’s nose and putting a gash on the back of his head, and Z gained an advantage that so terrorized Trayvon that he screamed for dear life for 40 seconds before Z finally shot him - all this without Trayvon showing signs of injury.
Does the Martin lawyer even have a hypothetical story? Does he claim there was a fight or wasn’t? If there was, was it before Z pointed a gun at Trayvon or after? How did Z get his injuries? Why didn’t Trayvon get any injuries?
What is clear from the timeline is that Trayvon had 3 minutes between the time Z “lost” him and when the confrontation began, yet the confrontation happened almost as far north as the first sighting of each other had happened, and to get home Trayvon needed to go south.