The alternative I suggested is based partly on the recording of the conversation between Zimmerman and the dispatcher a few minutes before the shooting, and partly on repports of what Zimmerman told family and friends (some of whom have appeared on Hannity's program). To follow Zimmerman's version, it appears that Zimmerman did not pull the gun out on his own but after Trayvon had knocked him down and was on top of him, he caught sight of the gun and tried to grab it.
A new piece of evidence yesterday was that Trayvon was at the store where he bought the skittles between 6 and 6:30. He had a 16-minute walk back to his father's place, so he had 20 or more minutes to spare either dawdling on the way or walking around the neighborhood in the rain looking at the houses--which is what he was doing when Zimmerman first saw him and reported him as someone behaving in a suspicious way.
Absent a new mystery eye-witness who is absolutely reliable we will never know the facts.
I am not willing to accept Zimmerman's version as anything but CYA. I would feel the same if the roles were reversed.