Trayvon Martin (Creative Commons)

Zimmerman had claimed self-defense in the shooting and told police he was the one screaming for help, but Tom Owen, a forensic consultant for Owen Forensic Services LLC, used voice identification software to rule out that possibility. Another expert using a different method arrived at the same finding.

Zimmerman, a Neighborhood Watch volunteer, shot Martin during a one-on-one scuffle on Feb. 26. Before the gunshot went off, one of them can be heard screaming on a neighbor's 911 call.

Owen said he used software called Easy Voice Biometrics to compare Zimmerman's voice to the voice in the recording. It returned a 48 percent match, but Owen said 90 percent or higher is needed to produce a positive match, The Sentinel reported.

"As a result of that, you can say with reasonable scientific certainty that it's not Zimmerman," Owen said.

However, Owen said he could not confirm the voice as Martin's without a sample of the victim's voice.

But another audio expert said he heard the 17-year-old's screams in the call, according to the New York Daily News. Ed Primeau, an audio engineer and forensics expert from Michigan said he relied on audio enhancement and his own ears to arrive at his conclusion.

"I believe that's Trayvon Martin in the background, without a doubt," Primeau said. "That's a young man screaming."

The experts' findings could provide yet another setback to Zimmerman's self-defense claim.

The volunteer watchman's friends have said that the 28-year-old broke his nose and had wounds on his head after a physical struggle with the teen. Police station video shot after the killing appeared to show Zimmerman without any visible injuries, according to the Daily News.

Zimmerman has been in hiding since Martin's death. Protesters marched through Sanford, Fla. on Saturday calling for his arrest.

Reach Executive Producer Danny Lee here, or follow him here.