Trayvon Martin's parents expressed relief Wednesday over a special prosecutor's decision to charge George Zimmerman, the man who shot and killed their unarmed 17-year-old son.

The Florida neighbourhood watch volunteer, who is now in police custody, has been charged with second-degree murder in the fatal shooting of the black teenager.

"We wanted nothing more, nothing less, we just wanted an arrest," said Martin's mother, Sybrina Fulton, in a brief appearance before the media.

"This is just the beginning. We got a long way to go," said Tracy Martin, the slain teen's father. "We will continue to hold hands on this journey — white, black, Hispanic, Latino" he added, calling for all to march "until the right thing is done."

A special prosecutor assigned to the case, Angela Corey, announced the charges at a news conference in Jacksonville, Fla.

"The team here with me has worked tirelessly for answers in Trayvon Martin's death," said Corey, who emphasized that the charges were not made due to mounting public pressure.

"There is a reason cases are tried in a court of law, not in a court of media."

New lawyer to invoke controversial defence

Zimmerman's new attorney, Mark O'Mara, said he will invoke Florida's "stand your ground" law in Zimmerman's defence, which gives people wide leeway to use deadly force without having to retreat in the face of danger. Florida is among 21 states with such a law.

George Zimmerman has been charged with second-degree murder in connection with the shooting death of 17-year-old Trayvon Martin. (Associated Press)

Zimmerman's shooting of the 17-year-old on Feb. 26 brought demands from black leaders for his arrest and set off a furious nationwide debate over race and self-defence that reached all the way to the White House.

"I cannot imagine living in George Zimmerman's shoes for the past number of weeks," said O'Mara, who added that his client has been the focus of a lot of anger, confusion and hatred.

"I'm expecting a lot of work and hopefully justice in the end."

The 28-year-old Zimmerman, whose father is white and whose mother is Hispanic, said the teenager attacked him. Martin's family members believe Zimmerman was the aggressor.

Zimmerman's former lawyers announced they were withdrawing from the case on Tuesday because they hadn't heard from their client since Sunday and didn't know where he was. They portrayed his mental state as fragile.

O'Mara disagreed, saying that Zimmerman "is very concerned about the charges, but he is OK."

"I'm not concerned about his mental well-being," he said.

Corey said a great deal of information on this case has been circulating that never should have been released.

"There's been an overwhelming amount of publicity in this case," she said, adding that she worries it will be difficult to find an impartial jury.

P.O.V. Do you think George Zimmerman can get a fair trial? Have your say.

"It is regrettable that so many facts and details have been released and misconstrued."

Corey said that two of her top prosecutors — Bernie de la Rionda and John Guy — would be leading the investigation, which she described as a truth-seeking mission.

"It was less than three weeks ago that we told those sweet parents we would get answers to all of their questions no matter where our quest for the truth led us," said Corey, who repeatedly stressed the importance of a fair and impartial trial.

"When we charge a person with a crime, we are equally committed to justice on their behalf as we are on our victim's behalf."

Slain teen's parents urge calm

Trayvon Martin's parents watched Corey's announcement on television in a room at the Washington Convention Center.

As soon as Corey uttered the words "second-degree murder," his mother and father grasped hands. Their attorney, Benjamin Crump, placed his hands over theirs. Fulton smiled slightly at the news.

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They appealed for their supporters, as well as Zimmerman's supporters, to remain calm in response to the prosecutor's decision.

"We've always said that we want peaceful resolution, no matter what side you're on," Tracy Martin said.

"We don't want them to stop the protest and the rallies, we just want to make sure that they remain peaceful," said Fulton.

"We're going through the process the right way, the proper way. We just ask that everybody that supports us do the same thing. Even the ones who don't support us, we want to make sure that they protest in a peaceful manner."

Earlier Wednesday Fulton said if she could speak directly to George Zimmerman, she would allow him a chance to say he is sorry for what happened.

"I would probably give him an opportunity to apologize," Fulton told The Associated Press in an interview.

"I would probably ask him if there were another way that he could have settled the confrontation that he had with Trayvon, other than the way it ended, with Trayvon being shot."

Trayvon Martin, who was killed in February, poses in an undated photo. (Martin family/Associated Press)

Her voice trailed off, and tears welled in her eyes. She expressed faith that the justice system would work as it should.

Martin offered several questions that he would like to ask Zimmerman about the sequence of events that led up to Trayvon's death, but in the end said he would want to know, "Was it really worth it?"

"The question I would really like to ask him is, if he could look into Trayvon's eyes and see how innocent he was, would he have then pulled the trigger? Or would he have just let him go on home?" Martin said.