SANFORD, Fla. -- A 911 call was at the center of a hearing leading up to George Zimmerman's trial for second-degree murder.
Attorneys were once again in court Friday ahead of Monday's jury selection.
Voice analyst expert Tom Owen testified via video conference that it was not Zimmerman screaming for help on the 911 call.
"The screams don't match at all," said Owen. "That's what tells me it's not George Zimmerman."
Owen said he analyzed the call using Zimmerman's recreation of the words "help" and "help me" to make the determination. He said he did not test if it was Trayvon Martin's voice because he did not have any recordings of it.
Owen did mention that it is easier to rule out a voice than to positively identify it.
On Thursday, the defense called an FBI expert who raised questions about the science a state expert used to claim Martin is the one heard screaming in the background of a 911 call.
The FBI expert said there is no accurate science to identify screams, and that only three seconds of the 45-second sample is not completely overshadowed by other sounds.
The expert said that would make it almost impossible to determine who was making the calls for help.
Zimmerman listened to the call with his head down in court.
Ultimately, Nelson will decide if the jury gets to hear the expert who is considered critical to the state's case.
Also on Thursday, O'Mara asked Nelson to allow the witnesses to give their testimony out of the public's eye.
He said the witnesses have concerns for their safety about testifying at the trial, which starts next week. He said their testimony could impact the jury's decision.
The state argued that if the witnesses are seen behind a screen that it might alarm the jury.
Nelson denied the motion.
At times, testimony grew testy -- especially when prosecutor Bernie de la Rionda questioned defense attorney Don West.
"We caught you hiding the information and confronted you about it, and you never gave it to us, and we called a witness today to prove that you hid that information and misrepresented it to the judge," West said to de la Rionda from the witness stand.
Zimmerman's defense team argued for sanctions against the State Attorney's Office for discovery violations. Nelson said she would handle any possible sanctions after the trial ends.
Zimmerman is charged with second-degree murder in the shooting death of Martin last year. The trial is expected to last more than a month.
Spurred by the trial and Martin's death, pastors in Sanford will hold a peace rally.
Peace Conference 2013 kicks off Friday at Fort Mellon Park and then moves to the First United Methodist Church.
Organizers say they want to discuss peace and injustice, creating a dialogue between "people who don't normally interact."