Trayvon Martin's mom: I heard my son screaming

A critical piece of evidence in the prosecution's case against George Zimmerman took center stage Friday when Trayvon Martin's mother took the stand to identify her son's voice in the background of a recorded 911 call.

For months leading up to the trial audio experts argued about the screams in the background of the call: Were they Trayvon's? Zimmerman's? Could they even be identified?

Earlier in the trial, FBI audio expert Hirotaka Nakasone testified that, on a recording as short and far away as the call in question, a person intimately familiar with the voice would be best able to identify it.

So state prosecutor Bernie de la Rionda put Sybrina Fulton, Trayvon's mother, on the stand and rolled the tape.

"That scream, do you recognize that?" he asked her, when it was over.

"Yes, it's Trayvon Benjamin Martin," she said.

In cross-examination, defense attorney Mark O'Mara asked if she was sure.

"Absolutely," she replied.

O'Mara asked Fulton if she was simply hearing what she wanted to on the tape, because it would mean Trayvon was not the agressor, as Zimmerman claimed.

"I heard my son screaming," she told him. "I didn't hope for anything. I simply listened to the tape."

Trayvon's older brother, Jahvaris Fulton, also heard the tape and identified his brother's voice.

Jahvaris Fulton said he had "heard him yell" before, but "not like that."

While the jury was out of the courtroom, O'Mara played a tape from a previous interview in which Jahvaris Fulton had said "I'm not sure" when asked about the voice on the tape.

"When I heard it in the mayor's office, I didn't want to believe it was him," Fulton said. "It was clouded by shock and denial and sadness. I didn't want to believe it was him."

Robert Zimmerman, George's father, has consistently claimed the screams on the tape were his son's.