the 911 call, in zimm's own words, show that trayvon is running away, and that zimm is chasing him.
60 seconds pass, then a physical confrontation and shooting.
The jury will have to decide if they truly believe ZImmerman really "gave up and started walking back" at the exact minute Trayvon "changed course and went into crazy attack mode".
Or, is the more likely outcome that in those 60 seconds, Zimmerman took the back way around a house, cut off trayvon, and they fought?
To me, it's not credible that both people instantly changed course in that one minute. More likely they continued on their actions from the 911 call, with zimm chasing and trayvon eluding. The jury will decide. There is no duty of prosecution to "prove" that minute of time - most cases that reach juries are very incomplete. They have to look at the pieces and decide what they THINK happened.
I can't exactly drag a kid into an alley, shoot his head off, then gloat "you can't PROVE what went on in that alley, so I walk!" Nope, if I created the situation, there's a missing window of time without witnesses, then I murder a mofo, I'm doing serious time...