By Barbara Liston
ORLANDO, Florida (Reuters) - A lawyer for a Florida man charged in the shooting death of unarmed black teenager Trayvon Martin is asking a judge to bar voice-recognition experts from testifying at his murder trial on grounds their techniques are not scientifically valid.
Prosecutors are expected to call audio experts to testify in the trial of George Zimmerman to analyze a 911 call made during the night when Martin was shot and killed. Zimmerman, a neighborhood watch captain, goes on trial June 10 on charges of second-degree murder.
One potential piece of evidence is expected to be a 911 call in which screams for help can be heard in the background during an altercation between Zimmerman and Martin before the shooting.
Zimmerman's family and supporters claim the voice is his, while Martin's parents insist the voice belongs to their son.
Last year, an FBI expert said a voice analysis of the call was inconclusive.
In a written motion made public on Monday, Mark O'Mara, Zimmerman's lawyer, argued against allowing voice analysts to testify.
"Scientific evidence presented to the court must be interpreted by the court as "generally accepted" by a meaningful segment of the scientific community in the particular field in which it belongs," O'Mara wrote.
O'Mara, who could not immediately be reached for comment, also wrote that the testimony could confuse the jury.
Ben Crump, lawyer for Trayvon Martin's parents, told Reuters the evidence is "absolutely" important for jurors to hear.
"The defense is concerned with the expert testimony because it supports what most have concluded, that Trayvon was screaming for help," Crump said.
Prosecutors say Zimmerman profiled and confronted Martin despite a police dispatcher telling him not to pursue the 17-year-old. Zimmerman, 29, has said the two fought and that he shot Martin because he feared for his life.
Two voice-identification experts retained by the Orlando Sentinel newspaper shortly after the killing ruled out Zimmerman as the person crying for help. Both experts quoted by the newspaper subsequently were added to the state's witness list.
Tom Owen, a nationally recognized audio expert who previously qualified as a court expert witness, used biometric software to analyze the cries for help. Owen told the Sentinel that he concluded "with reasonable scientific certainty that it's not Zimmerman."
The newspaper also retained Ed Primeau, a Michigan-based audio engineer and forensics expert, who used a combination of audio enhancement and human analysis based on forensic experience. Primeau told the Sentinel that the voice on the 911 tape was "a young man screaming."
"I believe that's Trayvon Martin in the background, without a doubt," the Sentinel quoted Primeau as saying.
Kenneth Marr, a specialist with the FBI's digital evidence laboratory in Quantico, Virginia, wrote in a report last year that the call was of insufficient voice quality and duration to conduct a meaningful voice comparison."
Of 18.82 seconds of screaming in the distance, only 2.53 seconds went uninterrupted by the conversation between the woman who called 911 and the dispatcher, Marr said.
Martin's father initially told investigators the voice was not his son's, although he subsequently identified the voice as Trayvon's after hearing it played through better equipment.
(Editing by Kevin Gray and Philip Barbara)