Who's voice is heard in the 911 calls?

Published On: Jun 07 2013 12:07:44 PM EDT

The George Zimmerman trial is scheduled to start this Monday, but Judge Debra Nelson is still deciding what jurors will be allowed to see and hear.

On Friday morning, a hearing in Sanford was held as the judge, prosecutors, and defense explored the science of voice recognition.

The hearing centers on a crucial 911 call where you can hear someone screaming in the background. Question is: Who is it? Zimmerman or Martin?

Audio expert Tom Owen testified via Skype. He was originally asked to review the 911 call by the Orlando Sentinel.

Owen compared the screams on that 911 call with the voice of Zimmerman yelling "help" in a videotaped reenactment he performed for investigators shortly after the shooting.

"The screams don't match at all," he told the court Friday, "so that's, that's what tells me that, okay, it's not George Zimmerman of the screams that I have presented."

SPECIAL SECTION: George Zimmerman Trial

SLIDESHOW: Evidence Photos

READ: Discovery documents

AUDIO: Witness hears person yell 'help' 15 times