SANFORD, Fla. (AP) -- Prosecutors face steep hurdles to win a second-degree murder conviction against neighborhood watch volunteer George Zimmerman in the shooting death of unarmed teenager Trayvon Martin, experts say.

Zimmerman was charged after a public campaign to make an arrest in the shooting that galvanized the nation for weeks. Now the prosecutor and her team will have to prove Zimmerman intentionally went after Martin instead of shooting him in self-defense, to refute arguments that a Florida law empowered him to use deadly force.

Zimmerman, 28, who turned himself in at a county jail Wednesday after prosecutor Angela Corey announced the charge, was to appear before a magistrate Thursday and plead not guilty in the Feb. 26 shooting of the 17-year-old that set off a nationwide debate about racial profiling and the rights to self-defense.

"He is concerned about getting a fair trial and a fair presentation," his attorney, Mark O'Mara said. "He is a client who has a lot of hatred focused on him. I'm hoping the hatred settles down ... he has the right to his own safety and the case being tried before a judge and jury."

Speaking Thursday on NBC's "Today" show, O'Mara said Zimmerman is stressed and very tired and hoping to get bail.

"He wants to be out (of jail) to be able to help with his defense, but overall he is doing OK," O'Mara told NBC.

Meanwhile, Martin's mother clarified what she meant by telling "Today" the case was an accident.

That comment left it unclear if she thought the shooting was accidental. But Fulton told The Associated Press that she was referring to the chance encounter between Zimmerman and her son.

"Their meeting was the accident," Fulton said. "That was the accident. Not the actual act of him shooting him. That was murder ... They were never supposed to meet."

Legal experts said Corey chose a tough route with the murder charge, which could send Zimmerman to prison for life if he's convicted, over manslaughter, which usually carries 15-year prison terms and covers reckless or negligent killings.

The prosecutors must prove Zimmerman's shooting of Martin was rooted in hatred or ill will and counter his claims that he shot Martin to protect himself while patrolling his gated community in the Orlando suburb of Sanford. Zimmerman's lawyers would only have to prove by a preponderance of evidence - a relatively low legal standard - that he acted in self-defense at a pretrial hearing to prevent the case from going to trial.

There's a "high likelihood it could be dismissed by the judge even before the jury gets to hear the case," Florida defense attorney Richard Hornsby said.

Corey announced the charges Wednesday after an extraordinary 45-day campaign for Zimmerman's arrest, led by Martin's parents and civil rights activists, including the Rev. Al Sharpton and the Rev. Jesse Jackson. Protesters wore hooded sweatshirts like the one Martin had on the night of the shooting. The debate reached all the way to the White House, where President Barack Obama observed last month: "If I had a son, he'd look like Trayvon."

Corey would not discuss how she reconciled conflicting accounts of the shooting by Zimmerman, witnesses and phone recordings that indicated Martin thought Zimmerman was following him.

"We do not prosecute by public pressure or by petition. We prosecute based on the facts on any given case as well as the laws of the state of Florida," Corey said.

Martin's parents expressed relief over the decision to prosecute the person who shot their son.

"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?" said his father, Tracy Martin.

Many attorneys said they had expected the prosecutor to opt for the lesser charge of manslaughter. The most severe homicide charge, first-degree murder, is subject to the death penalty in Florida and requires premeditation - something all sides agreed was not present in this case.

"I predicted manslaughter, so I'm a little surprised," said Michael Seigel, a former federal prosecutor who now teaches law at the University of Florida. "But she has more facts than I do."

O'Mara, Zimmerman's attorney, said his client would plead not guilty and invoke Florida's so-called "stand your ground" law, which gives people wide latitude to use deadly force rather than retreat during a fight.

The confrontation took place in a gated community where Martin was staying with his father and his father's fiancée. Martin was walking back in the rain from a convenience store when Zimmerman spotted him and called 911. He followed the teenager despite being told not to by a police dispatcher and the two got into a struggle.

Zimmerman told police Martin punched him in the nose, knocking him down, and then began banging the volunteer's head on the sidewalk. Zimmerman said he shot Martin in fear for his life. Sanford police took Zimmerman, whose father is white and whose mother is Hispanic, into custody the night of the shooting but released him without charging him.

A judge could dismiss the charge based on the "stand your ground" law, legal experts said. But some experts say the judge will also be under tremendous pressure to let the case go forward.

"Judges are not likely to take that out of the hands of the jury," said Florida defense attorney Randy Reep.

Other attorneys weren't surprised that Corey went for the maximum.

"Prosecutors look for leverage. They'll typically overcharge knowing that gives them wiggle room for plea discussions," said Derek Byrd, incoming president of the Florida Association of Criminal Defense Lawyers. "She knows that she could offer him manslaughter at some point or get in front of a jury that could split the verdict and agree on a lesser offense."

Corey wouldn't discuss how she arrived at the charges or disclose other details of her investigation. The prosecutor in Jacksonville was appointed to handle the case by Republican Gov. Rick Scott after the local prosecutor disqualified himself.

The U.S. Justice Department's civil rights division is conducting its own civil rights investigation.

Tensions had risen in Sanford, a town of 50,000 outside Orlando. Someone shot up an unoccupied police car Tuesday outside the neighborhood where Martin was killed. Outside of Sanford City Hall on Wednesday, Stacy Davis, who is black, said the arrest "is not a black or white thing for me. It's a right or wrong thing."

In Washington, Martin's family pleaded for calm in response to the decision. But Martin's mother, Sybrina Fulton, clasped hands and smiled in relief when she heard Corey utter the words "second-degree murder" on television.

"We wanted an arrest and we got it," Fulton said later. "Thank you Lord, Thank you, Jesus."

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Bluestein reported from Atlanta. Associated Press writers Suzanne Gamboa in Washington, Gary Fineout in Jacksonville, Fla.; Mike Schneider in Orlando, Fla.; Curt Anderson in Miami, Kyle Hightower in Sanford, Fla.; and Brendan Farrington in Tallahassee, Fla.; also contributed to this article.

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