A nighttime encounter on a quiet Florida street followed by hollering and pleas for help. Then a shot.

On Friday, the Sanford, Fla., police department released a flurry of 911 tapes from the night an unarmed black teenager, Trayvon Martin, was killed by a self-appointed neighborhood watch captain on patrol after a string of neighborhood break-ins.

The Feb. 26 shooting touched a nerve in a town that has in the past seen flare-ups of racial tension, raising the specter of racially-fueled profiling.

But when police refused to arrest the shooter, 28-year-old George Zimmerman, in the weeks that followed, those allegations became compounded by complaints that police, as one attorney said, “are letting a murderer walk the streets.”

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Sanford Police Chief Bill Lee has maintained that law enforcement has no evidence contradicting Mr. Zimmerman's story that he acted in self-defense. Complicating the situation for police, Florida has a so-called Stand Your Ground law that eliminates the need for someone who feels threatened to attempt to retreat, even in a public place. It's one of 17 states with such a law.

But amid growing public pressure to justify their decision to not arrest Zimmerman, police released seven separate 911 tapes ahead of a Monday court hearing on the topic.

“Completely devastated” by the content of the tapes, Trayvon's family and supporters say the tapes buttress their contention that far from fearing for his life, Zimmerman was an aggressor who confronted a young man peacefully going about his business and then shot him as the boy cried for help.

“This is amazing,” family attorney Natalie Jackson told the media after hearing the tapes on Friday. “The police have been covering up from the start. The most alarming thing was hearing a 17-year-old pleading for his life and someone still pulling the trigger.”

The tapes indicate that Zimmerman was in a resentful state of mind as he patrolled the neighborhood in the wake of several burglaries. At one point, Zimmerman tells the operator, “These [guys] always get away.”

But it's far from clear whether state investigators, who are reviewing the police department's decision, will be able to draw a different conclusion from local police. For one, police believe it was Zimmerman's voice, not Trayvon's, that can be heard yelling for help.

The at-times chilling tapes detail a series of events that began with Zimmerman calling 911 to report a “young black male” wearing a hoodie, walking about the Retreat at Twin Lakes gated community. It ended minutes later with panicked residents calling 911 to report an altercation, screams for help and a gunshot.

Describing seeing a man walking in the neighborhood, possibly on drugs, Zimmerman told the dispatcher, “It’s raining. He’s just walking around, looking about. He’s just staring ... at all the houses. Now he’s just staring at me.”

Then Zimmerman said the man had his hand in his waistband. “Something’s wrong with him. He’s coming to check me out.”

“Are you following him?” the dispatcher asks.

“Yeah,” Zimmerman said.

“We don’t need you to do that.”

As Trayvon's family sued for police to release the tapes and said in a Friday press conference that they had lost faith in the police department, Zimmerman's father, Robert Zimmerman, released a letter suggesting that Zimmerman did not exit his car as an aggressor, and that the news media were drawing the wrong conclusion about his son's state of mind.

At the time of the shooting, Trayvon was staying in the Retreat at Twin Lakes with his father and his father's fiancée to wait out a 10-day suspension from school. His family declined to say why the boy had been suspended, but said it wasn't for anything violent or criminal.

Trayvon had left his father's house, where he was watching a college basketball tournament, to go to a local convenience store, where he bought an iced tea and a bag of Skittles. He was on his way back to the house when Zimmerman spotted him.

To the family and their lawyers, the tapes and eyewitness account support their theory that Zimmerman had full control of the situation from the start.

“Racism doesn’t make you go get a gun and shoot someone,” Ms. Jackson, the family's lawyer, told the media. “Racism makes you profile them. What made him shoot was that he was one of them; he felt he was a cop.”

According to police, instead of heeding the dispatcher's warning, Zimmerman said he got out of his SUV to follow Trayvon. At that point, Trayvon came toward him and the two began to fight. Zimmerman said he ended up on the ground, where Trayvon punched him in the face. After yelling for help, Zimmerman said, he pulled his 9 mm gun from his waistband and fired.

While one eyewitness has said there was no scuffle, another has said he saw Zimmerman on his back on the ground. According to the police incident report, Zimmerman's nose was bloody and his shirt was grass stained.

Police also said that Trayvon's father, Tracy Martin, told them the voice pleading for help was not Trayvon. The family claims the police are lying, and pointed out that once the audio quality was cleaned up the father said that the voice did indeed belong to his son.

A family's grief, murky details, inconclusive audio, and a state law that makes it difficult for prosecutors to investigate subtleties of self-defense claims has made the situation difficult for police.

“The attitude is that we should just make an arrest and let a jury decide,” Chief Lee told the Miami Herald. “But to make an arrest, we would have to sign a sworn affidavit that we believe the case to be true. That would be irresponsible. We just do not have the evidence to disprove what Mr. Zimmerman says.”

Rep. Corinne Brown (D) of Jacksonville urged US Attorney General Eric Holder in a letter to investigate the shooting, referencing a history of racial tension in Sanford that goes back to when the city annexed the historically black town of Goldsboro in 1911 and changed street names that referenced the area's black pioneers.

“Given the history of racial tension in the Sanford community, I believe it would be wise for the Department of Justice to become involved and I request an emergency meeting with you or a senior DOJ official on Tuesday, March 20,” wrote Ms. Brown.

Even as the 911 tapes fail to provide hard proof of what happened in the moments before the shooting, one central question fuels the discontent: Had the roles been reversed, would Trayvon be walking free?

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