What about at the trial? Suppose the prosecution doesn't introduce any of Zimmeman's interviews - just relies on the NEN call, DeeDee, Sybrina and somebody who will testify that Zimmerman's gun killed Martin. How does the defense get the judge to give the jury a self defense instruction without Zimmerman testifying? Does Florida law allow the defense to introduce Zimmerman's out of court statements without him having to be cross examined on them?
The defense would use the NEN (showing GZ talking calmly to dispatcher), Dee Dee (who says TM lost GZ, was by his house, started walking back and is the first to confront GZ verbally), John and Austin who had GZ on the ground screaming for help, the 911 call capturing screams for help, injury reports, photos, witness saying he looked like he just got his butt kicked, etc. I'd think that would be plenty for reasonable doubt at trial.
I personally think GZ testifies at an immunity trial and not at regular trial. I'm not sure he has to testify to reach a preponderance of the evidence standard, but the one sticking point will be whether he started the conflict by doing something illegal. This will be dependent on Dee Dee's testimony. IF a judge only hears Dee Dee's statement and she repeats the claim that TM said "get off", then I'd think the defense would have to offer some evidence to counter that. Although, given that Dee Dee said "the man" had a deep angry voice, and some other things that could be disproved, the defense might be able to impeach her enough that the entirety of her testimony won't carry much weight. ITs even possible her testimony isn't allowed given the Martin's counsel involvement with her prior to law enforcement being given her name.
Lots of variables at play, but I think the injuries, screams for help and eye witness testimony gets GZ use of reasonable force without having to testify. The question I think would be whether he needs to testify in order to show he didn't instigate/start the violence. I think GZ wants to testify, but the defense team is smart enough to know that they aren't going to put him on the stand unless they feel its necessary.