That's possible. It's also why it's a shame that the only account of the story just happens to be the person who arose victorious from the struggle. No other evidence of the events leading up to the last moments of the fight/shooting so we are forced to either fit a story that fits his testimony, or do the opposite.
But we do have other evidence besides his account. Evidence which has been released. Although we don't know if all evidence has been released.
Evidence of eye witness testimony at various timelines along the incident. Both visual and audio witnesses.
Forensic evidence of the scene as well.
There is evidence out there. Some of which has been released and what we have been discussing.
The only really key points to this whole thing is the possibility of there being evidence that directly contradicts the account given thus far, and if that evidence was possibly covered up by the police, or not investigated properly in the first place. The fact we know of any evidence I find mind boggling at this point. As any case being built against someone is usually suppose to be kept on a need to know basis and not given to the media to cause these media style prejudgements from being cast. As was the case with the Duke Lacross team as an example given earlier.
So far, all the evidence released to the public has corroborated Zimmerman's account of the incident. Does that mean there is no evidence against his account we have not heard of yet? No, but that doesn't mean there is either. So to automatically speculate that Zimmerman is automatically guilty based upon the possibility of unknown or yet to be released evidence is stupid in my opinion.