How does the evidence point to GZ screaming? Because his friends and mom say it is him? Similar evidence points to it being Trayvon... right? It's all just opinions of each person's loved ones. Hardly evidence. How do we know it isn't Trayvon? Since Trayvon was the one that died, and GZ was the one who followed him with his gun locked and loaded, my opinion is that it could just as easily be Trayvon screaming. That doesn't make it evidence though, and surely doesn't make it fact.
I can easily see how this sort of testimony could be swayed by a bias or love for a person. I'm not great at explaining some thoughts, so bear with me...if I love someone and want them to get acquitted because I TRULY don't think they did something wrong, I can see how any doubt I had that it was my loved one could be turned to, "well, maybe it IS them? how would I know for certain that it isn't?" IMO, I think our brains can trick us into thinking something is one way when there is a possibility that it is actually another way. Just like Trayvon's mom is certain it's her son, and GZ's mom is certain it's HER son... one is either outright lying, or wants to so fiercely defend her child that her brain has convinced her that it is her son. There will be people who whole heartedly believe it is GZ screaming and people who honestly believe it is Trayvon Martin screaming... they can't all be right, so this evidence is kind of pointless since it cancels itself out, IMO.