Serino later said when cross examined by the prosecution that Zimmerman also said "that doesn't even sound like me" when asked about the screams.
Their testimony came after five of Zimmerman's friends and co-workers took the stand today and said it was Zimmerman's voice screaming for help seconds before he shot the teenager.
"It's Georgie," said family friend Sandra Osterman when asked about the screams. "I know it."
John Donnelly, who called Zimmerman a "dear friend," told the jury, "There is no doubt in my mind. That is George Zimmerman and I wish to God I did not have the ability to make the determination," he said, wiping his eyes.
Donnelly, a former Army medic during the Vietnam war, reinforced his opinion under cross examination.
"The voice screaming in that video is absolutely George Zimmerman, sir," he testified.
He rejected the suggestion that he would color his testimony to help his friend.
"This courtroom is about truth," Donnelly said.