Analysts: Questions surround 911 call analysis in Trayvon Martin case

Two experts who analyzed a 911 call made during the confrontation that ended in Florida teenager Trayvon Martin's death said they believe the screams heard in the background are not those of shooter George Zimmerman.

Zimmerman, 28, has claimed self-defense in killing Martin on February 26 in his gated community in Sanford, Florida, contending the teen punched him and slammed his head into a sidewalk before the shooting. But family and supporters of the 17-year-old victim asserted that Zimmerman racially profiled Martin, who is black, and ignored a police dispatcher's advice not to follow the teen.

Several neighbors phoned 911 around the time of the shooting, with the sound of someone yelling "help" evident on one such call before a gunshot rang out.

Expert analyses of those recordings to determine if the screaming voice is that of Zimmerman or Martin could end up being critical to the case, especially given that Zimmerman had told police he was crying out for help just before the shooting. But legal analysts say that there is no guarantee that such analyses would be ruled admissible in court if charges are filed and the case goes to trial.

The two men who detailed their findings Monday are established in the forensic audio field: Tom Owen is the chairman emeritus of the American Board of Recorded Evidence, while Ed Primeau is a longtime audio engineer who is listed as an expert in recorded evidence by the American College of Forensic Examiners International.

Before talking to CNN, both analyzed the recordings for the Orlando Sentinel using different tools and techniques. They came to the same conclusion: The man heard screaming is not Zimmerman.

"There's a huge chance that this is not Zimmerman's voice," said Primeau. "As a matter of fact, after 28 years of doing this, I would put my reputation on the line and say this is not George Zimmerman screaming."

Owens used cutting-edge software that is widely used in Europe and has become recently accepted in the United States, according to the recording evidence board's current chairman, Gregg Stutchman.

The software -- which uses sophisticated algorithms to match voices, based in part on things like the size and shape of a person's vocal chords or oral cavity -- found that the screaming voice in the last 911 call did not match Zimmerman's voice when he called police, a few minutes earlier, to report a "suspicious" person in the neighborhood. But is the analysis definitive enough for use in court?

David Faigman, a professor of law at the University of California-Hastings and an expert on the admissibility of scientific evidence, said courts and the overall scientific community have mixed opinions about the reliability of such "voiceprint" analysis.

And CNN and HLN legal analysts Beth Karas and Sunny Hostin raised questions about what the jury should consider before reaching a verdict.

Hostin says there are several questions and variables that must be considered, including the fact that the tests did not analyze similar speech. That is, the analysis was based on screams heard from a distance in a 911 call, compared with a direct phone conversation Zimmerman had with a 911 operator.

"Ideally, you want (Zimmerman or Martin's) voice saying the same exact thing, screaming 'help,' in order to analyze it," she said.

Stutchman said that matching up two voice samples, word-for-word, is ideal for some older voice analysis technology but not necessarily what his friend Owen used.

Beyond that, Karas questioned whether the test stood up to the voice comparison standards of the American Board of Recorded Evidence.

The standards indicate that when analyzing speech, there should be a minimum of at least 10 words to be compared with each other in order to say you can have a "possible elimination" conclusion. But in this case, the cries for help don't have nearly that number of words.

Owen said the published standards only partially apply to the kind of test he conducted.

"These standards apply to the older aural-spectrographic analysis and software," Owen said. "This only partially applies to the biometric software."

And the board's current chairman Stuchman concurred, saying this metric applies to some voice analysis technology, but not necessarily to that used by Owen. And Owen has had success in recent months convincing a judge that the new software is legitimate and accurate, according to his friend Stutchman.

Still, that doesn't mean there's any guarantee that tests in this case ever ever would be admissible in court -- or that it should be -- said Hostin.

"It really depends on the individual judge," she said. "In Florida, they are going to conduct a Frye test, the legal test, which asks if the

science is generally accepted in the community."

She and Karas furthermore urged caution before coming to a definitive conclusion as to who was screaming prior to Martin's shooting, even after the analyses posited by Primeau and Owen.

"I do think we need to take a step back, as with most of the facts in this case, and look at it the way the court would," Hostin said. "And that is by asking if the circumstances of how, and if, the test was done, OK, and wait to determine whether it's reliable."

CNN's Greg Botelho contributed to this report.

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