Outrage builds over Trayvon Martin shooting after release of police tapes

The tragic story of Trayvon Martin, the unarmed Florida teen who was fatally shot last month by a neighborhood watch volunteer, is now garnering national media attention. And the release last week of calls to police during the incident are bolstering demands for the shooter, George Zimmerman—who has yet to be detained by authorities—to be charged in Martin's death. Meanwhile, some are arguing that a permissive Florida gun law played a role in the tragedy. And Monday night came word that the U.S. Justice Department is probing the matter.

Here's what you need to know about where things stand:

What happened?
On Feb. 26, Martin, a 17-year-old African-American and Miami native, was visiting his father in Sanford, near Orlando. Martin was watching the NBA All-Star Game at a house in a gated Sanford community, and at halftime he stepped out to buy some Skittles and an iced tea at a local 7-Eleven.

Zimmerman, an armed neighborhood watch volunteer who was patrolling the area in an SUV, saw Martin returning to the house and became suspicious. A violent confrontation ensued, which ended with Martin being shot to death. Zimmerman was found bleeding from the nose and the back of the head, standing over Martin.

How did the police respond?
Zimmerman, a white Hispanic, told police he acted in self-defense, and has not been charged with a crime. "Until we can establish probable cause to dispute that, we don't have the grounds to arrest him," Sanford Police Chief Billy Lee said last Tuesday.

Martin's father has said that police initially told him they didn't charge Zimmerman because he studied criminal justice and had a squeaky clean record. (In fact, Zimmerman was charged in 2005 with battery on a law enforcement officer and resisting arrest with violence—the charges were later dropped.)

Police at the scene also didn't test Zimmerman for alcohol or drugs, although it's considered standard procedure in a homicide investigation to do so. And an eyewitness at the scene says she told cops that Martin had been calling for help, but that an officer "corrected" her to say that it was Zimmerman who was calling for help.

What about those tapes of calls to police?
Over the weekend, Sanford police responded to public pressure by releasing audio recordings of calls to police, as well as Zimmerman's own call to a non-emergency dispatch number.

The recording suggests Zimmerman followed Martin despite no evidence that the teen was doing anything wrong, and that Zimmerman ignored a warning to stay away. Zimmerman can be heard telling the dispatcher that he's seen a "real suspicious guy" who "looks like he's up to no good, or he's on drugs or something," adding: "These a------- always get away."

A few moments later, Zimmerman tells the dispatcher: "S---, he's running." The dispatcher asks: "Are you following him?" to which Zimmerman responds that he is. "OK, we don't need you to do that," the dispatcher warns.

There's little doubt that Zimmerman was overzealous in his neighborhood watch duties. In the eight weeks before the shooting, he had called police no less than 46 times.

What role did Florida's "stand your ground" law play?
Zimmerman was licensed to carry his gun. But Florida has some of the loosest gun laws in the country, allowing citizens like Zimmerman to patrol the streets armed, looking for crime. And in 2005, it passed what supporters refer to as a "stand your ground" law, which opponents call a "shoot first" law: It made it legal for Floridians to shoot to kill in response to a perceived threat, rather than first having to retreat before using deadly force.

Gun control advocates say the law condones the type of shooting that took Martin's life. "The 'shoot first' law seems to allow that sort of vigilante shooting," Daniel Vice, a senior attorney with the Brady Center to Prevent Gun Violence, a group that supporters stricter gun laws, told Yahoo News.

Supporters of the law say it doesn't give you a free pass to shoot first and ask questions later. "Stand your ground' is not a 007 license to kill," Sean Caranna of Florida Carry, a gun-rights group, told the Orlando Sentinel, adding that you have to have a "a real fear your life is in danger."

But Vice said that in reality, it's tough for prosecutors to prove a shooter didn't fear for his life, especially when he's the only one still alive to testify.

"Normally, if you shoot someone you have to explain it," said Vice. "This now completely shifts the burden and says, 'OK prosecutors, you now have to prove he didn't do it in self-defense.'"

What are the chances that Zimmerman will be charged?
The U.S. Justice Department said Monday night it had opened an investigation into the matter. "The department will conduct a thorough and independent review of all of the evidence and take appropriate action at the conclusion of the investigation," it said in a statement. "The department also is providing assistance to and cooperating with the state officials in their investigation into the incident."

If the Feds did get involved, they could potentially charge Zimmerman with a hate crime, if they believed that he singled Martin out because of his race.

The state of Florida also could still file charges.

What has been the public response?
The local state's attorney's office received so many emails urging it to prosecute Zimmerman that its website had to be taken down for 45 minutes, it told ABC News. And an online petition started by Martin's parents calling for Zimmerman's arrest has received more than 400,000 signatures. African-American leaders like Al Sharpton and hip-hop mogul Russell Simmons also have weighed in, and over the weekend New York Times columnist Charles Blow wrote that "as the father of two black teenage boys, this case hits close to home."

Update 8:30am, 3/20: This piece has been updated to reflect a breaking news development.

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