I'm not sure John's statement will help him prove SYG. John did not see the initial encounter only them on the ground. Just because he observed GZ on the bottom does not mean GZ was not the aggressor. It could very well be presented that TM was defending himself and trying to get away. John hightailed it into the house and locked the door behind him. Don't think he observed too much and was more worried about his own safety. So how good of a witness will he be??? jmo
Again, prosecution will have to prove Zimmerman's story is false (beyond a reasonable doubt) at trial. At least in theory that's how it should work.
John says he observed something that supports Zimmerman version of the story.
The prosecution will have to prove that wrong.