SANFORD, Fla. >> After declaring victories in getting federal and state officials to investigate the case of an unarmed black teenager shot to death by a neighborhood watch captain, civil rights leaders continued to pressure authorities to make an arrest.

At a town hall meeting Tuesday evening in Sanford, Fla., where the fatal shooting of 17-year-old Trayvon Martin took place last month, officials from the NAACP, the American Civil Liberties Union and the Nation of Islam urged residents to remain calm but demand that the shooter, George Zimmerman, be arrested.

Zimmerman has not been charged in the Feb. 26 shooting and has said he shot Martin, who was returning to a gated community in the city after buying candy at a convenience store, in self-defense after Martin attacked him. Police said Zimmerman is white; his family says he is Hispanic.

"I stand here as a son, father, uncle who is tired of being scared for our boys," said Benjamin Jealous, national president of the NAACP. "I’m tired of telling our young men how they can’t dress, where they can’t go and how they can’t behave."

The case has ignited a furor against the police department of this Orlando suburb of 53,500 people, prompting rallies and a protest in Gov. Rick Scott’s office Tuesday. The Justice Department’s Civil Rights Division said it is sending its community relations service this week to Sanford to "address tension in the community."

Earlier in the week, the federal agency opened a civil rights probe into the shooting, and in Florida, Seminole County State Attorney Norm Wolfinger said a grand jury will meet April 10 to consider evidence in the case.

"We are pleased the Department of Justice has heeded our calls and agreed to investigate this outrageous case," Jealous said in an emailed statement Tuesday. "The rules of justice in this nation have failed when an innocent teenage boy can be shot to death by a vigilante and no arrest is made for weeks."

At the town hall meeting, more than 350 people packed into the Allen Chapel AME Church. People jumped to their feet and cheered when local NAACP leader Turner Clayton Jr. said the federal Justice Department should not only review the investigation but also take over the Sanford Police Department.

Other civil rights leaders said the city’s police chief should step down.

"This is just the beginning of what is taking place," Clayton said. "We’re going to make sure justice prevails."

When The Associated Press tried to reach the police department Tuesday evening for comment, a dispatcher told a reporter to call in the morning.

Earlier Tuesday, an attorney for Martin’s family revealed the teenager told his girlfriend just moments before he was killed that he was being followed.

"’Oh he’s right behind me, he’s right behind me again,’" 17-year-old Trayvon Martin told his girlfriend on his cellphone, attorney Benjamin Crump said.

The girl later heard Martin say, "Why are you following me?" Another man asked, "What are you doing around here?’" Crump said.

Crump told reporters Tuesday Martin cried out when a man bearing a 9mm handgun came at him. Police said Zimmerman, who was found bleeding from his nose and the back of his head, told authorities he yelled out for help before shooting Martin.

"She absolutely blows Zimmerman’s absurd self-defense claim out of the water," Crump said of Martin’s girlfriend, whose name was withheld.

Martin, who was in town from Miami to visit his father in Sanford, called his 16-year-old girlfriend in Miami several times on Feb. 26, including just before the shooting, Crump said. The discovery of the lengthy conversations, including one moments before the shooting, was made over the weekend by Martin’s father, who checked his son’s cell phone log, Crump said.

The teenager told the girl on his way back from the store he’d taken shelter from the rain briefly at an apartment building in his father’s gated community, Crump said. Martin then told her he was being followed and would try to lose the person, Crump said.

"She says: ‘Run.’ He says, ‘I’m not going to run, I’m just going to walk fast,’" Crump said, quoting the girl.

After Martin encountered Zimmerman, the girl thought she heard a scuffle "because his voice changes like something interrupted his speech," Crump said. The phone call ended before the girl heard gunshots.

The last call was at 7:12 p.m. Police arrived at 7:17 p.m. to find Martin lying face down on the ground.

Zimmerman was handcuffed after police arrived and taken into custody for questioning, but was released by police without being charged. Police have interviewed Zimmerman twice since then.

Crump called the treatment patently unfair and asked if Martin would have received the same treatment if he had been the shooter.

"We will not rest until he is arrested. The more time that passes, this is going to be swept under the rug," Crump said.

Crump said he plans to turn over information about the call to federal investigators; a grand jury in Seminole County is also likely to subpoena the records. The Florida Department of Law Enforcement is also involved in the state case.

Former federal prosecutors said there are limitations to a Justice Department civil rights probe, which typically would involve a sworn law enforcement officer accused of abusing his authority.

In this case, they said, it’s not clear whether Zimmerman had any actual law enforcement authority or if the Sanford Police Department did anything improper. Zimmerman had a permit to carry a gun, but it was not required for his neighborhood watch patrol.

"I think the community has the feeling that there’s some type of cover-up," said Jeffrey Sloman, former U.S. attorney in Miami. "At least the department’s involvement makes sure it gets some review. He wasn’t a police officer. I’m sure that this is going to be a tough case to prosecute."

Authorities may be hamstrung by a state "Stand Your Ground" law that allows people to defend themselves with deadly force and does not require a retreat in the face of danger. Asked Tuesday if that law needs change, Republican Gov. Rick Scott said "it’s always positive to go back and think about existing laws."

During the town hall meeting in Sanford, Florida Rep. Geraldine Thompson promised the law’s repeal would be a top priority for the state legislature’s black caucus.

"If vigilante justice becomes the norm, will visitors feel comfortable coming to our state?" she said.

An online petition urging local authorities to prosecute Zimmerman had drawn more than 700,000 signatures at website Change.org as of early Wednesday. About 50 defense attorneys and protesters filled the lobby in the governor’s office Tuesday to deliver a letter seeking an independent investigation and a task force to study racial profiling. They applauded when Scott came out of his office to talk to them.

"I will make sure justice prevails," Scott said. "I’m very comfortable that (state law enforcement) is going to do the right thing. They’re not going to let somebody do something wrong and get away with it."

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Anderson reported from Fort Lauderdale, Fla. Associated Press writers Brendan Farrington and Brent Kallestad contributed from Tallahassee, Fla.