(CBS NEWS) - There are major developments in the case of a neighborhood watch captain in Florida, who shot and killed Trayvon Martin, an unarmed 17-year-old African American teen.
The U.S. Justice Department has now opened a civil rights investigation and the local Florida prosecutor has convened a grand jury to consider criminal charges, amid mounting public outrage, as CBS justice correspondent Bob Orr reports.
In the three weeks since Trayvon Martin was killed inside a gated Florida community, neighborhood watch volunteer George Zimmerman has maintained he shot Martin in self-defense.
But, attorney Benjamin Crump, who represents Martin's family, says the unarmed teenager was targeted because of his race. He is calling for Zimmerman's arrest.
Crump said, on the night of the shooting, Martin was heading home from the store and on the phone with his girlfriend. In a telephone interview, the young woman told Crump, she listened as Martin was suddenly confronted by a stranger.
According to the girlfriend, "Trayvon asked 'What are you following me for?.'" She said the man replied, "What are you doing around here?"
Martin's girlfriend said she urged him to run away. He said he would walk fast.
At around the same time, Zimmerman called the Sanford, Florida police to report a "suspicious person" in his neighborhood.
The 911 call paints a disturbing picture:
Operator:: "Are you following him?"
Operator: "We don't need you to do that."
What happened next is the critical question. A law enforcement source says Zimmerman told police he began retreating to his car, and only fired his weapon after Martin jumped him from behind.
Zimmerman has a license to carry a gun and Florida law allows people to use lethal force in self-defense.
But, Crump insists Zimmerman was the aggressor. Records show Zimmerman has been a frequent caller to police - with 46 calls since January, 2001 - often reporting African Americans.
Now, Tom Perez, who heads the Justice Department's Civil Rights Division says the government will determine if a hate crime may have occurred.
"We're conducting a thorough independent investigation of the facts and circumstances surrounding the death of Mr. Martin," Perez said.
Now, state prosecutors in Florida have a wider criminal investigation. If the grand jury returns an indictment, Zimmerman could face charges ranging from negligence on the low end to manslaughter, perhaps even murder. For now, Zimmerman remains free and has not yet been charged with any crime.
An earlier version of the story misstated the time frame which Zimmerman placed his many 911 calls. This version has been corrected to indicate they have taken place since January, 2001.