ORLANDO, Fla. (AP) -- Audio experts differ on whether screams for help captured on 911 calls are those of defendant George Zimmerman or of shooting victim 17-year-old Trayvon Martin, according to reports released Tuesday.

One New Jersey-based audio expert said in a report that the screams came from Martin, while another Florida-based audio expert said the shouts were a mix of Martin and Zimmerman.

Attorneys prosecuting Zimmerman on a charge of second-degree murder hired the audio experts to compare samples of Zimmerman's and Martin's voices with the shouts from the 911 calls phoned in by neighbors of Zimmerman. The residents of the gated community heard the neighborhood watch leader struggling with the South Florida teen during a confrontation last year. Determining whose voice was calling for help could aid a jury in deciding whether Zimmerman's claims of self-defense were justified.

Zimmerman is pleading not guilty and his trial starts next month.

Martin's family claims the voice is that of the South Florida teen, while Zimmerman's father has said in court he believes the cries are from his son.

Zimmerman's defense attorney, Mark O'Mara, has asked a judge to determine whether the audio analysis can be used at trial. O'Mara said in a filing that he was concerned the analysis of the 911 calls would prejudice jurors.

"Counsel has significant and legitimate concerns that such evidence will confuse the issues for this jury to decide, and it may well mislead the jury in this area of inquiry," O'Mara said in the filing.

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