Zimmerman said he lost sight of Martin, was returning to the truck and was attacked. That would fit this witnesses' account. At first Martins father claimed the voice yelling for help was not his son's. Allegedly he's now changed his mind.
It is clear the police had valid reasons for not arresting Zimmerman on that night. AFAIK they did not even hold him for questioning.
Doesn’t matter what the father says now. The witness says it was Zimmerman yelling for help.