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George Zimmerman trial: Trayvon Martin's father said voice on 911 call wasn't his son's, investigators testify

Sanford, Fla. police officer Chris Serino testifies as a defense witness in the George Zimmerman murder trial in Seminole circuit court, Monday, July 8, 2013 in Sanford. Photo by Joe Burbank-Pool/Getty Images

(CBS/AP) - Two police officers who investigated Trayvon Martin's shooting death testified Monday that the slain teen's father indicated to them the voice heard screaming in the background of a disputed 911 call did not sound like his son's.

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READ: Trayvon Martin Shooting: A timeline of events

Doris Singleton and Chris Serino, both investigators for the Sanford, Fla. police department, testified Monday afternoon for a second time in the trial of George Zimmerman, the former neighborhood watch volunteer charged in Martin's shooting death. Zimmerman claims he shot the teen in self defense.

On the witness stand, Serino said that he played the 911 call for Tracy Martin in the Sanford Police Department a few days after the fatal struggle on Feb. 26, 2012. After listening to the call - during which screams for help and a gunshot can be heard - Martin became emotional, Serino said.

Serino said he asked Tracy Martin whether or not the screaming voice sounded like his son's.

"It was more of a verbal and a non-verbal," Serino said. "He looked away and under his breath, as I interpreted it, said 'no.'"

VIDEO: Zimmerman trial: Prosecutor opens with profanity

Who was screaming on the call, placed by a neighbor, has been a key point of contention in the case. Seven witnesses have testified so far that the voice belonged to George Zimmerman. In contrast, Trayvon Martin's mother and brother testified it was the teen screaming.

Singleton, who witnessed the meeting, said, "I don't know his exact words, but [Tracy Martin] was telling Chris it was not his son's voice."

"He was very upset, he was very sad," Singleton testified. "He hung his head, he cried."

Singleton said she became "choked up" as she watched Martin listen to the tape.

"To know he was hearing the sound that ended his son's life was tough to watch," Singleton said. "...I can't imagine having to go through that because I have children. I can't imagine."

Under cross examination, prosecutor Bernie de la Rionda suggested that Tracy Martin may have been in denial about his son's death and that's why he uttered, "no."

"It could be perceived as denial," Serino said.

Also taking the stand Monday was Adam Pollock, owner of a gym where Zimmerman trained.

Pollock said Zimmerman didn't have the physical abilities to be able to box in a ring. He described him as "physically soft."

"He was an overweight, large man when he came to us, a very pleasant, very nice man, but physically soft - predominantly fat," Pollock said. "Not a lot of muscle. Not a lot of strength."

On cross-examination, Pollock said that Zimmerman lost between 50 and 80 pounds training at his gym and trained up to six hours a week. Prosecutors have argued that Zimmerman profiled Martin as a criminal and started the confrontation.

Defense attorneys asked Pollock to explain to jurors the mixed-martial arts fighting method called "ground and pound." The defense has said that Martin slammed Zimmerman's head into the sidewalk while he was on top of him in what neighbor John Good described as a "ground and pound" maneuver.

To demonstrate the move, gym owner Adam Pollock straddled defense attorney Mark O'Mara on the courtroom floor. Pollock testified that Zimmerman trained in the form of fighting known as grappling but was an unaccomplished fighter.

"He was about a 1," said Pollock, when asked to rank Zimmerman's athletic skill on a scale of 1 to 10.

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