The U.S. Justice Department is investigating possible hate crime charges in connection to a fatal shooting of an unarmed black teenager by a white neighborhood watch leader in the southern U.S. state of Florida last month.

Police have not arrested the shooter or charged him with a crime. A state grand jury will meet April 10 to consider all of the evidence. Meantime, tensions are running high in Sanford, Florida, the community where national attention has focused the spotlight on issues of racism and self defense.

The volunteer, George Zimmerman spotted Trayvon Martin as he walked to his father's home on a rainy night in the gated community. Zimmerman called police emergency, which recorded the conversation: 

Zimmerman: "This guy looks like he is up to no good, or he's on drugs or something. These [unintelligible] always get away. 

Dispatcher: "Are you following him ?"

Zimmerman: "Yes."

Dispatcher: "OK, we don't need you to do that."

But Zimmerman apparently followed Martin anyway. A short time later neighbors heard screams - then gunfire. 

Zimmerman says he shot Trayvon Martin in self defense after being attacked. Police have not charged him with a crime because of a Florida law known as "Stand Your Ground.’’ It gives people the right to protect themselves with deadly force, even outside of their homes. Martin's parents reject the self-defense claim. They say their son was targeted because he was black.

"If he had been white, he would not have been stopped. He would have not been approached at all," said Tracy Martin, the victim's father. 

Zimmerman's family says he is not a racist. But many African Americans say the case is about stereotypes of young black men as violent criminals. 

"How can you justify that shooting," asked one man.

The Sanford, Florida Police Department is under fire for its investigation. .

"If there were mistakes made we are going to handle that. We are going to act accordingly," said the city's mayor, Jeff Triplett

Authorities admit they overlooked evidence of what some believe was a racial slur that Zimmerman allegedly made before shooting Martin. "One certainly may argue that the statement coupled with the other evidence may cause the state attorney's office to start looking at a hate crime," said legal analyst Bill Schaefer.

Officers also failed to interview Martin's girlfriend. Phone records show she spoke to him moments before his death. She says he told her he was trying to get away from someone. 

"This claim that Trayvon Martin was the aggressor is preposterous, and it cannot be allowed to stand because we have all of the evidence now," said Martin family attorney Ben Crump.

Tensions in the small community are on the rise as civil rights leaders hold protest marches. Social media also are attracting national attention to the case. More than a million people have signed an on-line petition demanding Zimmerman's arrest. 

"I don't understand why this man [Zimmerman] hasn't been arrested. At least charge him and let a judge and jury decide if he is guilty," said Sybrina Fulton, Trayvon Martin's mother.

That won't bring her son back. But as federal and state authorities investigate the killing of Trayvon Martin, some lawmakers are questioning the law that allows people to defend themselves with deadly force.