During the brief appearance, Zimmerman stood up straight, looked straight ahead and wore a gray prison jumpsuit. He spoke only to answer "Yes, sir," twice after he was asked basic questions about the charge against him and his attorney.
His hair was shaved down to stubble and he had a thin goatee, which appeared consistent with his booking photo from the day before. He had resurfaced Wednesday to turn himself in after weeks in hiding.
Judge Mark E. Herr said he found probable cause to move ahead with the case and that an arraignment would be held on May 29 before another judge.
An prepared by prosecutors shed some light on why they chose to charge Zimmerman. The Orlando Sentinel said it had obtained the affidavit of probable cause before it was expected to be filed with the courthouse.
The newspaper says that Martin's mother identified screams heard in the background of a 911 call as her son's. There had been some question as to whether Martin or Zimmerman was the one calling for help.
Prosecutors also interviewed a friend of Martin's who was talking to him just before the shooting. The affidavit says Martin told the witness he was being followed and was scared.
Martin tried to run home, the affidavit says, but was followed by Zimmerman: "Zimmerman got out of his vehicle and followed Martin."
The affidavit says that "Zimmerman disregarded the police dispatcher" who told him to stop, and "continued to follow Martin who was trying to return to his home."
Speaking to reporters after the hearing, attorney Mark O'Mara said he was concerned that the case up to now has been handled in the public eye, with details coming out in piecemeal fashion.
"It's really supposed to happen in the courtroom," O'Mara said, deflecting questions about evidence in the case and his client's mental state.
Earlier Thursday on NBC's "Today" show, O'Mara said Zimmerman is stressed and very tired and hoping to get bail.
Meanwhile, Martin's mother raised eyebrows with her own comments on "Today" about the accidental nature of the case, but she clarified what she meant in another interview later in the day. Sybrina 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."
Zimmerman was charged after a public campaign to make an arrest in the Feb. 26 shooting, which has galvanized the nation for weeks. Some legal experts had expected Zimmerman to face a lesser count of manslaughter and say a prosecutor will face steep hurdles to win a murder conviction.
The prosecutor and her team will have to prove that the 28-year-old 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.
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 Wednesday. She was also present at Thursday's hearing.
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.