SANFORD, Fla. -

The attorney for George Zimmerman, the neighborhood watchman who shot and killed Trayvon Martin, said his client pleaded not guilty Thursday afternoon in the shooting death of Trayvon Martin.

Attorney Mark O'Mara, a former Local 6 legal expert, made the comments after his client's first appearance before Judge Mark E. Herr, who set Zimmerman's formal arraignment for May 29 at 1:30 p.m.

Zimmerman faces second-degree murder charges in Martin's death. Herr said he found probable cause for the charge.

Video: George Zimmerman arrives at jail

The only comment made by Zimmerman, who appeared attentive and calm while wearing a blue jail jumpsuit at the John E. Polk Correctional Facility, was, "Yes, sir," when asked if he was being represented by O'Mara.

The judge also agreed to temporarily seal witness documents containing contact information and statements, per O'Mara's request.

State Attorney Angela Corey attended the appearance, and afterward, prosecutors were asked why they decided to charge Zimmerman with second-degree murder, a charge that some experts believe may be difficult to prove.

"We charged what we thought was appropriate," prosecutor Bernie de la Rionda said.

O'Mara then talked to the media, saying his client is scared but is doing well mentally.

"He's frightened.  I'm not concerned, as some before me may have been, of his focus," said O'Mara, referring to Zimmerman's previous legal representatives, who stepped down Tuesday.

"I hope to have him released on bond," said O'Mara, who said he will file a motion to get a bond hearing. Local 6 had spoken to O'Mara earlier Thursday and he said he was filing a motion for a bond. But O'Mara said after speaking to Zimmerman he didn't have a safe place for him to go if he was released and that he was worried for his safety.

O'Mara also said Zimmerman doesn't have much money, and he's not aware how much money his client's website has garnered in donations.

"I think he's indigent for cost. He doesn’t have any money," O'Mara said.

O'Mara was also asked about Martin's mother, Sybrina Fulton, who said Thursday morning that the encounter between her son and Zimmerman was an accident.

"We're not going to be using the words against the mother of a deceased child," O'Mara said.

Meanwhile, officials released information on where Zimmerman is being held in jail, despite earlier statements that they wouldn't indulge in details. Deputies said he has been placed in administrative confinement, kept away from general population, according to a release.

Zimmerman's cell is designed to hold two inmates and is approximately 67 square feet. It has two beds and a toilet, along with a mattress, pillow, bed sheets and blanket.

Zimmerman arrived at the jail Wednesday night with Florida Department of Law Enforcement officials.  He was riding in a black SUV and covered his face from the media.  He was booked into the jail at 8:30 p.m. on a no bond status, records show.

Corey announced the charges against Zimmerman at a news conference in Jacksonville. Corey said Zimmerman turned himself in to FDLE authorities but wouldn't say where he was prior to that.

Watch Local 6 for more on this story.