Sanford, Florida (CNN) -- A case involving the fatal shooting of an unarmed Florida teen, which has sparked outrage and calls for justice, is in the hands of the state attorney's office.
Police say Trayvon Martin, 17, was returning from the convenience store to the home of his father's fiancee in a gated community in Sanford, Florida, around sunset on February 26.
A neighborhood watch captain, George Zimmerman, 28, saw the teen and called 911 to report a suspicious man, authorities said.
The 911 dispatcher told Zimmerman not to confront Martin, but by the time police arrived, the teenager lay dead with a gunshot wound in the chest, said Bill Lee, the Sanford police chief. He was carrying a small amount of cash, some candy and an iced tea.
Zimmerman told police he shot Martin in self defense, authorities said.
'Neighborhood watch' shooting racial?
Teen killed by neighborhood watch leader "When you add it up, it just doesn't even make sense," said Ben Crump, the Martin family's attorney. "Trayvon Martin, a kid, has a bag of Skittles. (Zimmerman) had a 9 mm gun. Trayvon Martin didn't approach George Zimmerman, George Zimmerman approached Trayvon Martin. So how can he now assert self defense?"
A gunshot can be heard on the 911 calls recorded that night, police said.
The Martin family has sought to make the tapes available, but State Attorney Norm Wolfinger said Tuesday the calls will not be made public until the investigation is complete.
"Trayvon Martin and his family, interested persons, and the public-at-large are entitled to no less than a through, deliberate and just review of the information provided, along with any other evidence that may or may not be developed in the course of the review process," Wolfinger's office said in a statement. "We intend to honor that commitment."
The shooting has sparked an outrage in the community, with some accusing Zimmerman, who is white, of profiling the black teenager.
Numerous CNN attempts to contact Zimmerman were unsuccessful, and it is unclear whether he has retained an attorney.
Police said they have not charged him because there are no grounds to disprove his story of what happened.
"The evidence and testimony we have so far does not establish that Mr. Zimmerman did not act in self defense. We don't have anything to dispute his claim of self-defense, at this point, with the evidence and testimony that we have," Lee said.
Lee said the 911 directions asking Zimmerman not to confront the teenager are not mandatory instructions.
"That is a call taker making a recommendation to him. He's not under a legal obligation to do that, so that is not something we can charge him with," he said. " But it would have been a good outcome ... if Trayvon Martin and George Zimmerman never came in contact with one another."
In a letter sent to U.S. Attorney General Eric Holder, the NAACP expressed doubt in the Sanford Police Department and asked the Department of Justice to review the case.
"The NAACP has no confidence that, absent federal oversight, the Sanford Police Department will devote the necessary degree of care to its investigation. We therefore call upon you to detail personnel to Sanford immediately to review the facts, ensure that the Sanford Police Department conducts an impartial, thorough and prompt investigation of the circumstances involving the death of this unarmed teen, and ensure that the responsible person is held accountable if a crime was committed," the letter said.