Week Three of the George Zimmerman trial began Monday with testimony from Zimmerman family friend Sondra Osterman, who testified that it was Zimmerman's voice screaming for help shortly before Trayvon Martin was killed.

Zimmerman attorney Mark O’Mara played back the contentious 911 call, which included a voice crying out for help. O'Mara then asked Osterman if she could identify the screaming voice.

“Yes, definitely. It’s Georgie,” Osterman replied. She was then asked why she was so sure it was Zimmerman’s voice and not that of Trayvon Martin, the 17-year-old who was later killed by Zimmerman. “I just hear it. I just hear him screaming.”

But state prosecutors in Florida Circuit Court in Sanford, Fla., attempted to damage Osterman’s credibility, getting her to say that she never heard Zimmerman scream in the same way as the voice screaming on the tape.

Prosecutor Bernie de la Rionda pointed out that Osterman wrote a book about Zimmerman and planned to donate profits from the book to Zimmerman.

“You have a stake in this, don’t you?” De la Rionda asked.

De la Rionda played the entire 911 call tape for Osterman, who said she heard Zimmerman saying, “these a-------, they always get away.”

De la Rionda asked how Osterman could be sure the screams for help came from Zimmerman if she never heard him scream that way before.

“I just felt that I knew it was him,” the Zimmerman family friend said. “And I knew the reaction his wife had when listening to it, it was George.”

On redirect examination, Osterman testified that Zimmerman’s voice was not tinged with anger or spite or that the neighborhood watchman was acting with ill will toward Martin.

Zimmerman faces second-degree murder charges in the killing of Martin, an unarmed black teen Zimmerman claims he shot in self-defense. The state disagrees, contending Zimmerman’s conduct amounted to murder.

The screams for help are seen as being crucial to the case. If the defense can convince the all-female jury that the screams came from Zimmerman, the jury is more likely to believe the defense’s argument that the killing was done in self-defense. However, if the jury is persuaded that the screams came from Trayvon, they’re more likely to convict Zimmerman.

The trial is in its third week. Zimmerman’s defense is expected to wrap up its portion of the case by Wednesday, according to Michael Skolnik of Global Grind. Skolnik indicated that the case may be in the hands of the jury by the end of the week and may render a verdict before the weekend.