[JoeRedskin]

As I understand it, the fight was on his front yard and he was very clear that guy A was on top of and beating guy B. He looked away/went for phone, heard a gunshot and then saw "the guy who had been on top" lying on the ground.

A man who witnessed part of the altercation contacted authorities.

"The guy on the bottom, who had a red sweater on, was yelling to me, 'Help! Help!' and I told him to stop, and I was calling 911," said the witness, who asked to be identified only by his first name, John.

John said he locked his patio door, ran upstairs and heard at least one gun shot.

"And then, when I got upstairs and looked down, the guy who was on the top beating up the other guy, was the one laying in the grass, and I believe he was dead at that point."

Trayvon Martin shot and killed in neighborhood altercation

The witness only wanted to be identified as "John," and didn't not want to be shown on camera.

His statements to police were instrumental, because police backed up Zimmerman's claims, saying those screams on the 911 call are those of Zimmerman.

Witness: Martin attacked Zimmerman

Sounds like he was pretty sure of what he saw and was close enough to speak to the two while they were fighting.