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SANFORD, Fla. -- Judge Debra Nelson is expected to make a case-changing ruling in the second-degree murder case against George Zimmerman.

She is expected to decide on whether voice expert testimony will be allowed about a 911 call made the night Trayvon Martin was killed.

"Mr. Owen took all these screams believing it was one person, stirred them up in a pot, ran them through a couple of times and came to some sort of opinion based on which light lit up," said defense attorney Don West.

Prosecutors are trying to prove that screams heard on 911 calls came from Martin, not Zimmerman.

The state's experts testified at an earlier hearing and said it was Martin heard screaming. The defense claims that positive audio recognition on the 911 call recordings isn't feasible.

Also, after nine days of jury selection, both sides decided on six females jurors to form the panel. Since the case is not a capital case, by Florida law, there is a six-person jury, as opposed to a 12-person jury.

"I wouldn't have predicated that because you want a diverse amount of opinion," said legal expert Jeffrey Deen.

All of the women chosen are mothers of different ages and five are white and one is Hispanic.