Much as the ridges of a human hand produce a fingerprint, each human voice has unique, distinguishable traits, Owen says. "They're all particular to the individual."
- STORY: What is difference between manslaughter and murder charges?
- Sign up for text alerts sent to your mobile phone
- PHOTOS: Pictures: Key players in the case against George Zimmerman
- Pictures: George Zimmerman's many faces
- Pictures: Trayvon Martin through the years
- Pictures: George Zimmerman released on bail
See more photos »
Sanford, FL, USA
The technology Owen used to analyze the Zimmerman tape has a wide range of applications, including national security and international policing, he said. A recently as January, Owen used the same technology to identify accused murderer Sheila Davalloo in a 911 call made almost a decade ago.
Owen testified that it was Davalloo, accused of stabbing another woman nine times in a condo in Shippan, Conn., who reported the killing to police from a pay phone in November 2002.
Davalloo was convicted, according to news reports.
Owen says the audio from Zimmerman's call is much better quality than the 911 call in the Davalloo case. Voice identification experts judge the quality based on a signal-to-noise ratio; in other words, comparing the usable audio in a clip to the environmental noises that make a match difficult.
And the call on which the screams are heard is better quality than is necessary, Owen says.
"In our world, that's the home run," he says.
Not all experts rely on biometrics. Ed Primeau, a Michigan-based audio engineer and forensics expert, is not a believer in the technology's use in courtroom settings.
He relies instead on audio enhancement and human analysis based on forensic experience. After listening closely to the 911 tape on which the screams are heard, Primeau also has a strong opinion.
"I believe that's Trayvon Martin in the background, without a doubt," Primeau says, stressing that the tone of the voice is a giveaway. "That's a young man screaming."
Zimmerman's call to authorities minutes before the shooting provides a good standard for comparison, Primeau says, because it captures his voice both at rest and in an agitated state.
Only one person alive knows exactly what transpired in the moments immediately before Trayvon was fatally shot: Zimmerman, who has claimed he fired in self-defense.
Zimmerman told police he was walking back to his SUV after a brief foot pursuit of Martin, and the teen confronted and attacked him, punching him and slamming his head into the pavement.
Arriving police said Zimmerman was bloodied. One officer wrote in a police report that he overheard Zimmerman telling a paramedic, "I was yelling for someone to help me, but no one would help me."
Angela Corey, the special prosecutor assigned to the case, has yet to decide whether to charge Zimmerman, send the case to a grand jury or decide against charging.
If Zimmerman's self-defense claim is tested at trial, legal experts say a forensic identification of the voice in the 911 audio could be key evidence, either in Zimmerman's favor or to his detriment.
Still, Maine-based audio enhancement expert Arlo West says that today's juries sometimes seem reluctant to accept evidence that's any less conclusive than what they're used to seeing on television.
"I call it the 'CSI' effect," he says, referring to "CSI: Crime Scene Investigation," the popular — if not always realistic — forensics-based TV drama. "You get in front of a jury, and they expect a miracle."
email@example.com or 407-420-5171