http://www.sanfordfl.gov/investigation/docs/Twin%20Lakes%20Shooting%20Initial%20Report.pdf
On youtube I came across a witness that looked down from his second-story window at the scene and saw the fight, Zimmerman screaming and asking for help. He told Zimmerman that he was calling 911 right now for help.
Then they played a 911 call, perhaps from this witness, that has the screaming on it. It is a high-pitched, very frightened screaming (sounded almost like a girl!).
Another youtube was interviewing a “witness” that said she heard the screaming of a child, a bang, and then the screaming stopped. She then went on to say how tragic that this child was killed in cold blood. Of course only hearing it doesn’t give the full picture. The screams DO sound like from a child (or girl like I thought) - but based on the “EYE”witness they were in fact Zimmermans.