By Barbara Liston
ORLANDO, Florida (Reuters) - An FBI expert found crucial evidence in the Trayvon Martin case was inconclusive, saying it was impossible to tell if the voice screaming for help belonged to the black Florida teenager or his shooter George Zimmerman just before the neighborhood watch captain pulled the trigger.
That detail came from a mass of evidence made public on Thursday in the case that sparked civil rights protests across the United States and debates over guns, self-defense laws and race relations in America.
The documents confirm numerous compelling facts and minutiae that have been debated at kitchen tables and on television sets across the country following the February 26 homicide when Zimmerman, 28, shot and killed the 17-year-old Martin.
Police initially declined to arrest Zimmerman, citing Florida's "Stand Your Ground" self-defense law, but a special prosecutor who was subsequently appointed charged Zimmerman with second-degree murder. Zimmerman has pleaded not guilty.
The nearly 200 pages of documents plus photographs, videos and audio recordings provide evidence that will be seized upon by both Zimmerman's supporters and his detractors, including the revelation that Martin had traces of marijuana in his system and a witness who described the teen as beating on Zimmerman in the style of mixed martial arts.
But what may be the central point of contention - who screamed for help? - goes tantalizingly unanswered.
If it was Zimmerman, it would confirm his story that he pleaded for assistance against the teenager who was brutally beating him. If it was Martin, it could establish Zimmerman was the aggressor who shot an unarmed teenager and would be a major component of a case for second-degree murder.
Relatives of both Zimmerman and Martin swear it was their kin who was pleading for his life.
The cries for help were silenced by a single shot from Zimmerman's Kel Tec 9mm handgun but not before they were recorded on phone calls that neighbors made to police to report a struggle between two men in their gated community in the central Florida city of Sanford.
"Critical listening and digital signal analysis further revealed that the screaming voice of the 911 call is of insufficient voice quality and duration to conduct a meaningful voice comparison with any other voice samples," concluded Kenneth Marr, a specialist with the FBI's digital evidence laboratory in Quantico, Virginia.
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 in his report.
Moreover, the audio sample was "produced under an extreme emotional state," the report said, making it difficult to analyze.
Zimmerman supporters can point to a separate Sanford police report within the documents that says Martin's father, Tracy Martin, told investigators the screams did not belong to his son when he heard the recordings two days after the shooting.
Martin has since told reporters he was uncertain at that time, but that when he heard an enhanced recording on March 16 he was convinced it was his son calling for help. The boy's mother, Sybrina Fulton, also insists the cries come from Trayvon.
Zimmerman's father and brother have been equally adamant it was George's voice they heard.
"That is absolutely, positively George Zimmerman," father Robert Zimmerman said in an interview with prosecutors on March 19. "Myself, my wife, family members and friends know that is George Zimmerman. There is no doubt who is yelling for help. It is absolutely my son."
MOUNDS OF EVIDENCE
The documents made public on Thursday include reports from law enforcement, the medical examiner who performed the autopsy, and fire department medics who treated Zimmerman at the scene.
There are photographs of the crime scene and Zimmerman's injuries, plus audio recordings of witness statements, and video of Zimmerman arriving at the police station and the last images of Martin alive, while he was buying candy and a soft drink at a convenience store.
Alongside photos of Zimmerman's bloody scalp and puffy nose, the documents say Zimmerman repeatedly declined to be taken to the hospital to be treated for injuries suffered in his scuffle with Martin, which could weaken his argument that he feared for his life and required deadly force to defend himself.
In addition, the medical examiner's report showed only a small abrasion on Martin's left ring finger and no other injuries - apart from the fatal gunshot wound to the chest - to support Zimmerman's claim he was nearly beaten to death.
A Sanford police officer said "Zimmerman appeared to have a broken and bloody nose and swelling of his face," which could support Zimmerman's contention he feared for his life.
Zimmerman told the fire department medics he was taking temazepam, a medication to treat anxiety or insomnia, and librax, which is prescribed for gastrointestinal disorders.
According to ABC News, a medical report by Zimmerman's doctor also said he had been prescribed Adderall, which is used to treat Attention Deficit Hyperactivity Disorder (ADHD).
Police also conclude the incident was "ultimately avoidable" had Zimmerman remained in his car that night instead of following Martin.
The medical examiner's report showed traces of THC - the active ingredient in marijuana - in Martin's blood and a positive test for 'cannabinoids' in his urine.
An attorney for the Martin family called the marijuana evidence irrelevant, saying it was more telling that police declined to order a drug or alcohol test of Zimmerman.
Martin was on suspension from school at the time of the shooting after school officials found traces of marijuana, but no actual drugs, in his belongings.
"The relevant thing is George Zimmerman didn't have a toxicology report so we don't know what he had in his system," said attorney Benjamin Crump. "We know he (Zimmerman) was on prescription medication but we don't know if he was taking it or not and what effect that would have on him."
(Additional reporting by Tom Brown and David Adams; Writing by Daniel Trotta; Editing by Peter Cooney, Todd Eastham and Lisa Shumaker)