It could be that Zimmerman continued to look for Martin after he didn't know where he was. In any case, when he did see Martin again, no magical event happened that separates all that had gone before from all that followed. It was another moment in a fluid situation that is comprised of numerous facts your account selectively omits. These facts will not be omitted at trial, and additional facts will almost certainly be presented.
As you point out, we don't know what happened with much certainty. So we should wait to hear the evidence. We do know that GZ admits to shooting TM to death. There are numerous issues to consider before determining what level of legal responsibility GZ bears for his actions. GZ must show that his actions were not reckless if he is to avoid a conviction on some charge.
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justitia omnibus
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"It ain't what you don't know that gets you into trouble. It's what you know for sure that just ain't so."