(CNN) -- Trayvon Martin's girlfriend, talking to him on the telephone, heard the teenager saying, "get off, get off" in the moments before his cell phone cut off and he was shot dead, according to a recording of the girl's interview with a prosecutor released Friday.

Another witness, however, seems to put Martin on top of George Zimmerman for at least part of the struggle, according to another recording released Friday.

"Where I first walked out there, the black guy was on top and the only reason I can tell that was because the guy that was on the ground under him at that point wrestling was definitely a lighter color," the witness, whose name has not been made public, said in the interview.

Martin was African-American. Zimmerman is white and Hispanic.

The recordings provide the most detailed look yet into previously reported witness statements detailing the last moments of Martin's life.

Martin was shot to death February 26 while walking in the Sanford, Florida, neighborhood where he was staying during a visit with his father.

Zimmerman, a neighborhood watch volunteer, is charged with second-degree murder in the death, which sparked nationwide protests and inflamed public passions over race relations and gun control.

The girl, whose name has not been made public, told Assistant State Attorney Bernie de la Rionda that Martin got away from the man, who turned out to be Zimmerman, but only temporarily.

He was out of breath from running away, and scared, she said, and decided not to keep running because he was close to the house where he was staying.

And as Zimmerman drew closer, the girl said, Martin called out," Why you following me for?" according to the recording.

"I hear this man, like this old man, say, 'What are you doing around here?'" the girl said.

The girl said she called out to Martin, asking what was happening, but he didn't answer. The next thing she heard was a bumping sound, followed by what might have been a scuffle.

"I could hear it a little bit, 'Get off, get off,' then the phone just hung up," the girl said.

The other witness said he heard loud noises outside his home that dark, wet night, and when he looked outside, he saw one person in dark clothing over someone who appeared to be wearing a red or white piece of apparel.

"I heard, 'Help, help, help,' and I yelled at them and said, 'Hey cut it out,' " the witness told police. He then called 911.

Zimmerman has claimed self-defense in the shooting, saying Martin charged him after the two exchanged words, knocking him to the ground and hitting his head repeatedly against a concrete sidewalk.

Prosecutors say Zimmerman profiled Martin, an African-American teenager wearing a hoodie, as a criminal and killed him, even though he was doing nothing wrong.

The witness said he couldn't say what sparked the incident.

"I didn't see how it started, I didn't see how it ended. I just saw the part where they were in an altercation on the ground," the witness said.

The recordings released Friday are the latest in a series of revelations from the official investigation into the shooting. Authorities are making details of the case publicly available as attorneys prepare for Zimmerman's trial.

Also released this week was a document filed with prosecutors by Sanford police two weeks after the shooting, urging Zimmerman's arrest.

"The encounter between George Zimmerman and Trayvon Martin was ultimately avoidable by Zimmerman, if Zimmerman had remained in his vehicle and awaited the arrival of law enforcement, or conversely if he had identified himself to Martin as a concerned citizen and initiated dialog (sic) in an effort to dispel each party's concern" the police request to arrest Zimmerman said. "There is no indication that Trayvon Martin was involved in any criminal activity."

Other documents released this week include Martin's autopsy report, a fire department report on Zimmerman's injuries and an FBI analysis of emergency calls in which someone can be heard screaming in the background.

The autopsy report showed that Martin died of a gunshot wound to the chest fired from within 36 inches and that he had traces of marijuana in his blood and urine.

In his 911 call just before the shooting, Zimmerman had speculated that the teen looked like he was "up to no good or he's on drugs or something."

Martin's blood contained THC, which is the psychoactive ingredient in marijuana, according to autopsy results released Thursday. The autopsy was conducted February 27, the day after the teenager was shot dead.

Toxicology tests found elements of the drug in the teenager's chest blood -- 1.5 nanograms per milliliter of one type (THC), as well as 7.3 nanograms of another type (THC-COOH) -- according to the medical examiner's report. There also was a presumed positive test of cannabinoids in Martin's urine, according to the medical examiner's report. It was not immediately clear how significant these amounts were.

No precise levels on the urine were released.

Dr. Michael Policastro, a toxicologist, cautioned against reading too much into the blood THC levels, adding that one cannot make a direct correlation between those findings and a level of intoxication.

He also said that levels of THC, which can linger in a person's system for days, can spike after death in certain areas of the body because of redistribution.

And Dr. Drew Pinsky, an addiction specialist who hosts a show on CNN's sister network HLN, added that marijuana typically does not make users more aggressive.

Concentrations of THC routinely rise to 100 to 200 nanograms per milliliter after marijuana use, though it typically falls to below 5 ng/ml within three hours of it being smoked, according to information on the National Highway Traffic Safety Administration's website.

While some states have zero-tolerance policies for any drug traces for driving while impaired, others set certain benchmarks, the website of California's Department of Alcohol and Drug Programs notes. In Nevada, that equates to 2 ng/ml for THC and 5 ng/ml for THC-COOH, also known as marijuana metabolite. The cutoff level in Ohio is 2 ng/ml for THC and 50 ng/ml for THC-COOH.

Martin's father, Tracy, had taken his son with him to Sanford, about four hours away from the boy's home and where the father's fiancee lived, after the teen was suspended for 10 days from Michael M. Krop High School in Miami.

According to records obtained by The Miami Herald, Martin had been suspended from school three times: once for writing graffiti on a door, another time for school truancy and the last time because of drug residue found in his backpack.

Just before the shooting, Zimmerman, 28, called 911 to complain about a suspicious person in his neighborhood.

In the call, Zimmerman said he was following Martin after the teen started to run, prompting the dispatcher to tell him, "We don't need you to do that."

Prosecutors say Zimmerman disregarded the advice, leading to a confrontation between the two.

Much has been made about whether Zimmerman during that call used a racial epithet in referring to Martin. But an FBI analysis, released Thursday, determined that the word could not be definitively identified "due to weak signal level and poor recording quality."

A screaming voice could be heard on other 911 calls placed by neighbors, with some speculating that those screams came from Martin and others that they belonged to Zimmerman. The FBI did not make a final determination either way, citing several reasons, including the fact they came during "an extreme emotional state," that there weren't enough words to make a good comparison and that the sound quality was low and distant.

Zimmerman claimed, according a police report released earlier, that he'd been "assaulted (by Martin) and his head was struck on the pavement."

According a report from the Sanford Fire Department, released Thursday, Zimmerman had "abrasions to his forehead," "bleeding/tenderness to his nose," and a "small laceration to the back of his head" when emergency personnel arrived at the scene at 7:27 p.m., six minutes after they were first called.

By that time, Martin had no apparent pulse, according to the fire and EMS report. Emergency personnel attempted mouth-to-mask resuscitation and chest compressions, to no avail. He was pronounced dead at 7:30 p.m.

Prosecutors have said Zimmerman killed the unarmed teenager after unjustly after profiling him. Zimmerman, who has pleaded not guilty, has said that he shot Martin in self-defense.

The start of the trial hasn't been set.

The case put a spotlight on race relations, spurring protests nationwide and drawing prominent civil rights leaders to central Florida denouncing the actions of Sanford police and calling for Zimmerman's arrest. Special prosecutor Angela Corey announced he'd been charged on April 11, weeks after Sanford police initially declined to do so.

The case also raised questions about gun laws, as well as the merits of the "stand your ground" law in Florida and similar laws in other states that allow people to use deadly force anywhere they feel a reasonable threat of serious injury or death.

CNN's Vivian Kuo and Danielle Dellorto, and InSession's Jessica Thill contributed to this report.

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