Neighborhood watch volunteer George Zimmerman, who is set to face second-degree murder charges in the death of an unarmed black teen, will plead not guilty at his first court appearance scheduled for Thursday at 1:30 p.m., his lawyer said.

Speaking on NBC's "Today" show, Mark O'Mara, Zimmerman's new lawyer, said his client 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 said.

Florida special prosecutor announced Wednesday that she concluded that claims of self defense were not supported in the shooting death of 17-year-old Trayvon Martin.

Special prosecutor Angela Corey's announcement marked a turning point in the high-profile case, as weeks of outrage and speculation about Zimmerman's motives culminated in his arrest -- something that Martin's family and their supporters have argued for since the Feb. 26 shooting in a gated community in Sanford, Fla.

O'Mara said he is "hoping that the community will calm down" after the intense scrutiny of the case in the community and the media drove Zimmerman into hiding.

Zimmerman, 28, was booked Wednesday evening into the Seminole County Jail, and he could face a minimum of 25 years in prison or a maximum of life if convicted.

In announcing the arrest, Corey would not discuss how she reconciled the conflicting accounts of what happened or explain how she arrived at the charges, saying too much information had been made public already. But she made it clear she was not influenced by the uproar over the past six weeks.

"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.

A second-degree murder charge in Florida is typically charged when there is a fight or other confrontation that results in death and where there is no premeditated plan to kill someone.

Meanwhile, Martin's parents said charges against Zimmerman in the killing of their son would start the healing process, but they won't stop fighting until the shooter is convicted.

"We just wanted an arrest and we got it," Martin's mother, Sybrina Fulton, said.

"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?" father, Tracy Martin, said.

The shooting brought outspoken demands from black leaders for Zimmerman arrest and set off a furious nationwide debate over race and self-defense that reached all the way to the White House. Martin was black. Zimmerman's father is white and his mother is Hispanic.

One of the biggest hurdles to Zimmerman's arrest over the past month was Florida's "stand your ground" law, which gives people wide leeway to use deadly force without having to retreat in the face of danger. The lack of an arrest had sparked outrage and rallies for justice in the Orlando suburb and across the country.

Many legal experts had expected the prosecutor to opt for the lesser charge of manslaughter, which usually carries 15 years behind bars and covers reckless or negligent killings, rather than second-degree murder, which involves a killing that results from a "depraved" disregard for human life.

The most severe homicide charge, first-degree murder, is subject to the death penalty in Florida and requires premeditation -- something that all sides agreed was not present in this case.

The confrontation took place in a gated community where Martin was staying with his father and his father's fiancee. In phone calls, Zimmerman told an emergency dispatcher that Martin looked suspicious, and he followed the teen despite the dispatcher's advice.

Zimmerman's father said that Martin threatened to kill his son and that Zimmerman suffered a broken nose. A video taken about 40 minutes after the shooting as Zimmerman arrived at the Sanford police station showed him walking unassisted without difficulty. There were no plainly visible bandages or blood on his clothing, but Zimmerman may have had a small wound on the back of his head.

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

Zimmerman had been in hiding for weeks, his former lawyers, Craig Sonner and Hal Uhrig, said.

"He is largely alone. You might even say he is emotionally crippled by virtue of the pressure of this case," Uhrig said.

The U.S. Justice Department's civil rights division is conducting its own investigation. But federal authorities typically wait until a state prosecution is complete before deciding how to proceed.

The Associated Press and NewsCore contributed to this report.