Published: May 14, 2013 11:53 PM EDT

ORLANDO, Fla. (AP) - Audio experts gave differing opinions on whether screams for help captured on 911 calls were those of neighborhood watch leader George Zimmerman or the 17-year-old teen he fatally shot last year.
    
One audio expert said in a report released Tuesday that the screams came from Trayvon Martin, while another audio expert says the shouts were a mix of Martin and Zimmerman.
    
Attorneys prosecuting Zimmerman for second-degree murder hired the audio experts to compare samples of Martin and Zimmerman's voices with the shouts from the 911 calls.
    
Martin's family claims the voice is that of the South Florida teen. Zimmerman's father has said in court he believes the cries are from his son.
    
Zimmerman is pleading not guilty, claiming self-defense. His trial starts next month.