Sybrina Fulton joins Democratic lawmakers at the state Capitol and calls for the repeal of Florida's Stand Your Ground law.
UPDATE: The mother of Trayvon Martin has testified that screams for help captured on audio of a 911 call came from her 17-year-old son.
Sybrina Fulton took the witness stand Friday morning during the trial of George Zimmerman, the former neighborhood watch volunteer charged with murder in Martin's shooting death. Zimmerman has pleaded not guilty and says he shot the teen in self-defense during a fight.
WATCH: Sybrina Fulton's testimony
After the audio was played, prosecutor Bernie de la Rionda asked Fulton, "Who do you recognize that to be?" She replied, "Trayvon Benjamin Martin."
Identifying the screams on the 911 call could be critical to the case because it may help determine who was the aggressor during the scuffle between Zimmerman and Martin.
Sanford, Florida -- We could see a pivotal and emotional moment in the trial of George Zimmerman on Friday. One of Trayvon Martin's parents is expected to take the stand.
Experts are saying it will likely be Martin's mother, Sybrina Fulton, and she would be called up for a very specific reason: she knows the sound of her son's voice.
It ties together with this 911 call. In the background, you can hear screams for help -- and then a gunshot.
The last time they were in court, jurors heard from an FBI audio expert. He said it's not possible from the limited audio available for scientists to tell who is screaming for help, Martin or Zimmerman.
But someone who knows the screamer? That's a different story. He said someone who knows the person who's screaming may be able to to identify them.
That's why it's believed Martin's mother will be called to the witness stand: to tell the jury, that it's her son crying out for help in his last moments.
Her testimony would help paint the picture that George Zimmerman was the aggressor -- not defending himself -- when he followed Trayvon Martin, then shot and killed him during a struggle.
Zimmerman told police he was the one calling for help, although it's not clear whether he will tell the jury that himself. We don't know whether he'll testify in his own defense during the trial. Zimmerman faces life in prison.
The emotional words of Martin's mother may be the last thing jurors hear before the prosecution rests its case.
The state is expected to hand things over to the defense Friday, and defense witnesses may be taking the stand by the end of the day.
You can watch the entire George Zimmerman trial streaming live on wtsp.com and on our free 10 News iPad app.
Grayson Kamm, 10 News