West didn’t probe that aspect very much, but the witness said that extreme stress causes physical changes that cannot be faked by an actor, and that sort of stress was present in the recording. Whoever was screaming felt genuine, extreme fear.
That by itself indicates it was the person on the bottom screaming. It also gives direct evidence of the state of mind of one of the two - extreme stress / fear of death. Since the other physical evidence indicates Zimmerman was the only one with a valid reason for any fear, I think it shows Zimmerman’s state of mind at the time of the shooting - and it provides direct evidence that Zimmerman acted legally. The law doesn’t require you to be in certifiable fear of your life, only that you be genuinely afraid of death or severe injury.