Here is how I would rebut MOM's close (which has been pretty good when I've watched it).
"There were only two witnesses to the totality of this incident. One of them is George Zimmerman. The only other possible witness, unfortunately, is Trayvon Martin. He can't tell you what happened. But you are not obligated to accept the self-serving, unsworn, characterization of this confrontation offered by George Zimmerman. We have presented ample evidence that his account is simply not credible.
And absent any credible, unbiased account of this entire confrontation, we are left with the same facts we have had at the beginning. A trained, armed, larger defendant fatally shot an unarmed, smaller teenage victim. Reasonable doubt is not the absence of all doubt. And the defense has offered no credible evidence that Mr. Zimmerman feared death or great bodily harm, much less that reasonably cautious and prudent person in his situation would have."