George Zimmerman scheduled for first appearance in court, attorney Mark O'Mara to ask for bail

(CNN) -- The attorney for George Zimmerman plans to ask a judge as early as Thursday to allow the neighborhood watch volunteer charged with killing an unarmed, black teen to post bond -- though he believes it will be difficult.

"My hope is that the judge will grant a bond, and that it'll be a bond that the family can make," attorney Mark O'Mara said Wednesday. "They are not a family of means. So that's going to be difficult to begin with, and that conditions are that you stay local, I think that may be difficult."

"I think nobody would deny the fact if George Zimmerman is walking down the street today he would be at risk," he said.

Zimmerman, 28, who had been in hiding, turned himself in Wednesday after authorities said they will charge him with second-degree murder in the February 26 shooting death of 17-year-old Trayvon Martin.

The charge against Zimmerman marks a turning point in a case that triggered a nationwide debate about race in America and about Florida's "stand your ground" law -- which allows people to use deadly force anywhere they feel a reasonable threat of death or serious injury.

O'Mara said Zimmerman, who will plead not guilty, is worried about getting a fair trial in Sanford -- where thousands have converged to join in protests calling for his arrest and decrying the police department's handling of the case.

"We simply wanted an arrest; we wanted nothing more, nothing less," said Martin's mother, Sybrina Fulton, after the charge was announced.

Charge amid a see-saw of allegations

Forty-six days after the shooting, a special prosecutor assigned to the case announced the charge against Zimmerman on Wednesday. During that time, the calls for "Justice for Trayvon" had grown louder and louder, with Martin's supporters taking to the streets and to the web.

"Let me emphasize that we do not prosecute by pressure or petition. We prosecute cases based on the relevant fact of each case and on the laws of the state of Florida," said Prosecutor Angela Corey, who has a reputation for taking on tough, controversial cases in the three counties that make up the 4th Judicial Circuit.

Corey said whether the case is decided by a judge or jury, "I can assure they will only get the relevant, admissible evidence on which can then base their decisions."

Prosecutors usually level a second-degree murder charge when they accuse someone of a killing that is not premeditated or planned. It carries a maximum sentence of life in prison.

In severity, the charge falls between first-degree -- when a person is accused of killing someone deliberately -- and manslaughter, when an act results in an unintended death.

Corey did little to put to rest questions that have swirled around what happened the night Martin was killed in the suburban Orlando community. Witnesses and attorneys for both sides have offered conflicting accounts.

What is known is that Martin, wearing a hoodie, ventured out from his father's fiancee's home in Sanford to get a snack at a nearby convenience store. As he walked home with a bag of Skittles and an Arizona iced tea, he was shot and killed by Zimmerman.

Sanford police questioned Zimmerman and released him without charges.

From there, the case has evolved into see-saw allegations by Zimmerman's supporters, Martin's family and authorities.

Zimmerman says he killed Martin in self-defense after the teen punched him and slammed his head on the sidewalk, according to an Orlando Sentinel report that was later confirmed by Sanford police.

One of the responding officers saw a wound on the back of Zimmerman's head and a bloody nose, and noted that his back was wet -- indicating he had been lying in the grass, according to the police report.

An enhanced copy of a surveillance video showing him in police custody after the shooting appears to show a bump, mark or injury on his head.

Martin's family and supporters have dismissed the video.

They say Zimmerman, who is Hispanic, racially profiled the teen, who was black, and ignored a police dispatcher's directive not to follow him.

Zimmerman's attorneys, who he has since replaced, interpreted the call differently, and say the operator did not order Zimmerman not to follow.

A recording of a 911 call made the night of the shooting captured someone pleading for help. Zimmerman has said he was yelling for help, according to his family members and his account to authorities.

Martin's relatives have said they are certain the voice heard on the 911 call is Martin's.

Audio experts, who analyzed the recordings for the Orlando Sentinel using different techniques, said they don't believe it is Zimmerman.

They compared the screams with Zimmerman's voice, as recorded in a 911 call he made minutes earlier describing a "suspicious" black male.

The debate was further muddied when a witness, who declined to be identified by CNN, said she saw and heard the incident through her window.

When pressed if she could determine who

was yelling, the witness said "It was the younger, youthful voice (rather) that it was the deep voice I heard when they were arguing."

Zimmerman's initial attorneys questioned the account, saying it was dark at the time of the shooting.

Martin's family has said a Sanford police detective filed an affidavit saying he did not find Zimmerman's statements after the shooting credible -- but that Sanford Police Chief Bill Lee and State Attorney Norm Wolfinger met the night of the shooting and disregarded the detective's advice.

Neither Sanford police nor prosecutors have confirmed the existence of such an affidavit. And Wolfinger vehemently denied that such a meeting occurred.

The two sides have also debated what Zimmerman whispered under his breath during his 911 call.

Martin's supporters said he uttered a racial slur; one of Zimmerman's former lawyers said he told them he whispered "punks."

O'Mara not a stranger to high-profile cases

O'Mara replaces Craig Sonner and Hal Uhrig. They told reporters Tuesday that they had lost contact with their client and no longer represent him.

O'Mara said the family contacted him after referrals from other lawyers.

He is a well known criminal defense attorney who is no stranger to high-profile cases and TV cameras.

In 2004, he successfully defended Shamir Suber, who was charged with second-degree murder for plowing into the back of a car and killing its driver while trying to evade police. Suber was eventually convicted of the lesser charge of manslaughter.

Zimmerman was alone Wednesday when he turned himself in to the Florida Department of Law Enforcement's office in Jacksonville, said department spokeswoman Joyce Dawley.

George Zimmerman's brother, Robert Zimmerman Jr., told CNN's "Piers Morgan Tonight" that the family was "devastated" by the development.

"There were no winners in this already," the brother said.

Zimmerman had been in hiding since shortly after the shooting. His family and former attorneys said he feared for his life.

At one point, the New Black Panther Party offered a $10,000 bounty offer for his capture, despite vehement opposition from, among others, Martin's family.

"There's a lot of issues and there's a lot of emotions and we need to calm this down," O'Mara said. "It needs to be tried in a courtroom, which is the only place it's supposed to be tried, and that's what I'm going to try help get done."

Authorities have said Zimmerman was not immediately charged because there were no grounds, at the outset, to disprove his account that he'd acted to protect himself.

The case has drawn comments from President Barack Obama -- a father of two girls who said, "If I had a son, he'd look like Trayvon" -- and led to protest marches in cities and campuses across the country.

Officials urge restraint

O'Mara asked there be no rush to judgment.

"Nobody, after all, wanted Trayvon Martin to be pre-judged as he was walking down that street," he said. "I ask you not to pre-judge George Zimmerman, and please do not pre-judge the criminal justice system. It's going to work. We just need to let it work."

Gov. Rick Scott, who appointed the special prosecutor on the case, issued a statement Wednesday calling on Florida's residents to "allow our justice system to reach an appropriate conclusion in this case."

Meanwhile, Attorney General Eric Holder pledged Wednesday that the Justice Department. which is running a concurrent investigation launched three weeks ago, will "conduct a thorough and independent review of the evidence."

"I know that many of you are greatly -- and rightly -- concerned" about Martin's death, Holder said -- "a young man whose future has been lost to the ages."

At a barber shop in west Sanford, an area that has served as a gathering point for Martin protesters, Demetrius Hastings watched a live broadcast of Corey's announcement.

"It's good to see they are doing what they finally did. I don't know who is to blame," Hasting told CNN. "But this shouldn't happen again."

CNN's Martin Savidge and Vivian Kuo, and InSession's Beth Karas, Jessica Thill and Aletse Mellado contributed to this report.