SANFORD, Fla. -- Jurors in the George Zimmerman trial are heading into their weekend with a lot of courtroom drama and conflicting testimony to digest.

Friday's action-packed session saw the prosecution rest its case, and the judge reject a defense request to acquit Zimmerman of second-degree murder in the fatal shooting of 17-year-old Trayvon Martin last year.

The mothers of both Martin and Zimmerman listened to the same 911 recording of someone screaming for help, and each said she was convinced the voice was that of her own son.

The question of whose voice is on the recording could be crucial to the jury in deciding who was the aggressor in the confrontation between the neighborhood watch volunteer and the teenager.

"I heard my son screaming," Martin's mother, Sybrina Fulton, said firmly after she was played a recording in which distant, high-pitched wails could be heard in the background as a Zimmerman neighbor asked a dispatcher to send police. Moments later on the call, there was a gunshot and the crying stopped.

Gladys Zimmerman, though, testified she recognized the voice all too well: "My son." Asked how she could be certain, she said: "Because it's my son."

Martin's half brother, 22-year-old Jahvaris Fulton, testified that the cries came from the teen. And Zimmerman's uncle, Jose Meza, said he knew it was Zimmerman's voice from "the moment I heard it. ... I thought, that is George."

After Friday's session was over, defense attorney Mark O'Mara told reporters "there will be a lot of other witnesses" who will testify that the voice on the call is George Zimmerman's.

"But we'll just present the case," he said. "We're just getting started."

Gladys Zimmerman was the defense's first witness. O'Mara said he expects to call "several" of the state's 38 witnesses back as well when trial resumes Monday, and he left open the possibility that he would try to introduce toxicology evidence showing Martin had marijuana in his system at the time he died. Judge Debra Nelson has denied the admission of that evidence for the time being.

O'Mara may also call witnesses who he says have stated that Zimmerman was not a racist. Part of the prosecution's theory is that Zimmerman profiled Martin as one of the young black men he'd called law enforcement about as being possible suspects in burglaries in his townhome community weeks prior to the shooting.

O'Mara said he could rest his case as soon as next week.

Immediately after the state rested Friday, he asked Nelson to acquit Zimmerman, arguing that the prosecution had failed to prove its case.

O'Mara said an "enormous" amount of evidence showed that Zimmerman acted in self-defense, and he argued that Zimmerman had reasonable grounds to believe he was in danger, and acted without the "ill will, hatred and spite" necessary to prove second-degree murder.

But prosecutor Richard Mantei countered: "There are two people involved here. One of them is dead, and one of them is a liar."

Mantei told the judge that Zimmerman had changed his story, that his account of how he shot Martin was "a physical impossibility," and that he exaggerated his wounds.

After listening to an hour and a half of arguments from both sides, Nelson refused to throw out the murder charge, saying the prosecution had presented sufficient evidence for the case to go on.

Earlier in the day, Sybrina Fulton introduced herself to the jury by describing herself as having two sons, one of whom "is in heaven." She sat expressionless on the witness stand while prosecutors played the 911 recording.