Are there any witnesses that are going to contradict any prosecutorial testimony with their own eye/ear witness accounts, or is the defense all discrediting these witnesses and possibly Zimmerman testifying?
Their initial accounts all contract their current accounts. They all seem to remember more as time goes on. And none of their accounts are definitive. They are all full of doubt and even speculation. Identifying screams from people they don't know through building walls, and the same person who can't tell the difference between one shot and three shots. Identifying people by who appeared bigger in the dark, but misindentifying who was wearing the darker clothes. One person say they were running north, the other saying south. There is not one solid account of the events.
Is this really all that uncommon for criminal case eye witnesses? And enough to convict - rightly or wrongly in run of the bill cases every day?
In my own experience, most witnesses "improve" their accounts and leave themselves open for some impeachment, but doing post-conviction work, I've seen a lot of guys convicted on the testimony of unreliable witnesses. Of course, those defendants likely had worse lawyers than Zimmerman.
My own impression is that few of these witnesses matter all that much. As a matter of law, it is true that the State must prove every element of the crime, including the lack of a self defense defense, beyond a reasonable doubt. But I just don't think it works that way in practice (and in fact, it couldn't). Because so much of this case is undisputed (i.e., that Zimmerman did shoot Martin and that Martin was unarmed), I just think that the Defense's evidence is going to mean a lot more than the State's evidence.
That doesn't mean that the defense will need to put Zimmerman on the stand (although I'd say that it's rare not to do so in a self defense defense), but they'll have to present expert testimony that looks at forensic evidence and reconstructs the crime scene and timeline and that makes more sense than the State's presentation. Again, this arguably is against what the law says because theoretically Zimmerman shouldn't have to carry the burden of proof. But my own impression of that is that only really matters to the extent that a trial judge gives an improper jury instruction on that element.