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Judge in George Zimmerman trial to rule: Can experts testify about 911 calls?

The yells and pleas audible on several 911 calls could provide clues about whether George Zimmerman murdered Trayvon Martin. The judge in the case will decide whether audio experts can give the jury their analyses of the calls.

In one analysis of 911 tapes that record Trayvon Martin鈥檚 last moments alive, his killer, George Zimmerman, is deemed to utter a cryptically religious aside 鈥� 鈥淭hese shall be鈥� 鈥� and then Trayvon is interpreted as yelling, 鈥淚鈥檓 begging you鈥� and 鈥渟top!鈥�

That analysis, put forward in a May 15 report by audio expert Alan Reich, a state forensics consultant, is potentially devastating for Mr. Zimmerman鈥檚 defense, whose trial is to begin Monday.

On Thursday, the Seminole County circuit judge presiding over the case, Debra Nelson, begins two days of hearings on whether the jury can consider that analysis 鈥� or whether it is, as critics suggest, 鈥渧oodoo forensics鈥� that should be discarded as hearsay.

The hearing will also take up whether other analyses of the 911 calls should be weighed by the jury. But the analysis by Mr. Reich is considered the key one at issue.

Since Trayvon can鈥檛 testify at the trial and the majority of eyewitness accounts are murky at best, the snippets of voices that can be heard deep in the background of several 911 calls have held crucial but elusive clues for a central question the jury will be deciding: Did Zimmerman truly fear for his life when he fired, or did the older man control the situation and fire at a helpless and defensive Trayvon?

The judge already ruled earlier this week that the following are not admissible in court: texts, social-media conversations, and photos that show Trayvon referencing pot and guns and indicating a proclivity for getting into fights.

Zimmerman is charged with second-degree murder in the fatal shooting of Trayvon, an unarmed black teenager, on Feb. 26, 2012. A volunteer watchman in a gated Sanford, Fla., neighborhood, Zimmerman described Trayvon, who was wearing a hoodie, as suspicious and followed him despite being told by a 911 dispatcher to wait for police.

After a brief fight, Zimmerman shot Trayvon point-blank in the chest, claiming self-defense. Zimmerman received lacerations to the back of his head and a broken nose from the altercation with Trayvon 鈥� the key evidence, besides his own account, that his defense says proves that he鈥檚 not guilty.

According to Zimmerman鈥檚 account, he pulled out a 9mm pistol from his pants as he lay on his back being pummeled by a person he believed to be a possibly armed adult.

The audiotapes have already been controversial. Media companies hired experts shortly after the shooting to analyze Zimmerman鈥檚 911 call to the police, where he described Trayvon as 鈥渟uspicious鈥� and at one point complained about 鈥渢hese [expletive], they always get away.鈥� Zimmerman has sued one network for allegedly altering the audio to make it sound like he uttered a racial slur, which most experts now agree he did not.

Born in the midst of World War II intelligence operations, audio forensics have become a crucial law-enforcement tool, employing a whole cadre of experts across the globe who use techniques like adaptive filtering and voice biometrics to decipher and decode hard-to-hear or hard-to-understand recordings. They charge up to $4,500 to analyze an hour鈥檚 worth of recording and up to $2,500 per hour for court time.

A number of audio experts have gone over the available tapes, especially two recordings known as 鈥淐all 1鈥� 鈥� Zimmerman鈥檚 call to the dispatcher 鈥� and 鈥淐all 3鈥� 鈥� a 911 call from a resident where voices can be heard in the background. Most have agreed that a scream for 鈥渉elp鈥� at the end of Call 3 is Trayvon鈥檚 voice.

In his analysis, Reich, too, matches that voice to Trayvon, though he hears the word 鈥渟top鈥� instead of 鈥渉elp鈥� before a shot rings out.

Martin鈥檚 voice, Reich concludes in his May 15 report, 鈥渋s younger and he generates much of what some observers have called screams.鈥� He continues, 鈥淭he two males are engaged in a loud, purposeful, mostly 鈥榯urn-taking鈥� linguistic dialogue. The speech associated with the confrontation is often quite difficult to understand, but is amenable to individualized digital enhancement and computer-aided transcription, using an interactive, segment-by-segment approach.鈥�

Zimmerman鈥檚 lawyers will fight to bar the analysis by Reich, who likens Zimmerman's vocalization at one point to that of a 鈥渃arnival barker.鈥�

Robert Zimmerman, Zimmerman鈥檚 brother, told CBS News on Wednesday that Reich 鈥渋s hearing what no one else is able to hear.鈥� He added, 鈥淓xperts that reach conclusions that can鈥檛 be re-created by any other person flies in the face of the very definition of science.鈥�