SANFORD, Fla. — A judge denied a defense request to delay the start of George Zimmerman’s trial, which began Monday with potential jurors filling out confidential questionnaires and a scattering of protesters gathering outside the courthouse to support the family of the teen Zimmerman shot during a confrontation last year.

The selection of jurors who both the prosecution and defense believe can be objective in the highly publicized case is expected to take all week.

Judge Debra Nelson said the jury selection would alternate with the continuation of a hearing to determine whether she will allow the testimony of voice-recognition experts who say they might be able to identify who was screaming on a 911 tape recorded during Zimmerman’s confrontation with Trayvon Martin.

Thus far, the experts have reached mixed conclusions. Defense attorneys don’t want them to testify.

In her first order of business, Nelson denied a request by defense attorney Mark O’Mara to delay the trial on second-degree murder charges because he needed several more weeks to prepare.

O’Mara blamed prosecutors for a delay in turning over evidence and said he needed time to interview an attorney for Martin’s family. “We’re not fully ready and need more time,” O’Mara said.

Prosecutors opposed the request for a delay.

The trial was taking place in the Orlando suburb of Sanford, Fla., the scene of massive protests last year by people who were angered that police waited 44 days before charging Zimmerman with second-degree murder. Other demonstrations were held around the country, and the case drew worldwide attention as it fanned a debate about race, equal justice under the law and gun control.

Potential jurors began the day by filling out a confidential questionnaire.

There is no dispute Zimmerman shot an unarmed Martin, 17, during a fight on a rainy night in February 2012. Prosecutors will try to show the neighborhood watch volunteer racially profiled the black teenager, while Zimmerman’s attorney must convince jurors Zimmerman pulled his 9 mm handgun and fired a bullet into the high school student’s chest because he feared for his life.

Zimmerman, who identifies himself as Hispanic, says he shot Martin in self-defense. If convicted, he could get a life sentence.

Under Florida’s “stand your ground” law, Zimmerman, 29, could shoot Martin in self-defense if it was necessary to prevent death or great bodily harm. O’Mara previously decided not to invoke a “stand your ground” hearing in which a judge alone would decide whether to dismiss the case or allow it to proceed to trial.

Martin’s father, Tracy Martin, expressed relief that the trial was starting.

“We seek a fair and impartial trial,” he told reporters Monday. “We ask that the community continue to stay peaceful as we place our faith in the justice system.”

Law enforcement officials at the Seminole County Courthouse had been anticipating scores of protesters supporting either Martin’s family or Zimmerman. But the crowds stayed away on the first day of the trial, with just a little more than a dozen protesters showing up. They included relatives of Oscar Grant, a man who was fatally shot by an Oakland, Calif., police officer in 2009, and members of a Communist Party group.

Cephus Johnson, Grant’s uncle who flew in from California, said he wanted to stand with Martin’s family at the start of the trial.

“We know how important it is to be embraced by families who have gone through the same things,” Johnson said.

Wearing a hoodie similar to the one Martin had on when he was shot, Noche Diaz, a leader of the Revolutionary Communist Party, and about 10 other party activists carried placards that said “We Say No More.” Diaz said it was important for protesters to have a presence at the trial’s start since “if people waited in the first place, there wouldn’t be a trial.”

Tierrel Mathis, a Florida A&M law student who wanted to observe the start to one of the highest-profile trials in central Florida, was surprised there weren’t more protesters.

“I thought there would be mobs of people,” Mathis said.

Randy McClean and David Hill two Orlando-area defense attorneys, predicted prosecutors will attack Zimmerman as a frustrated, would-be police officer who had a chip on his shoulder. Zimmerman was employed at a mortgage risk management firm. He had studied criminal justice at a community college and had volunteered to run his community’s neighborhood watch program.

“The state’s narrative is going to be … Zimmerman was a powerful neighborhood watchman, a wannabe officer who liked to use his authority,” McClean said.

The Feb. 26, 2012, confrontation began when Zimmerman spotted Martin, whom he did not recognize, walking in the Retreat at Twin Lakes, the gated townhome community where Zimmerman lived and the fiancee of Martin’s father also resided. There had been a rash of recent break-ins at the Retreat, and Zimmerman was wary of strangers walking through the complex. He was well-known to police dispatchers for his regular calls reporting suspicious people and events.

Martin was walking back from a convenience store after buying ice tea and Skittles. It was raining, and he was wearing a hoodie.

Zimmerman called 911, got out of his vehicle and followed Martin behind the townhomes despite being told not to by a police dispatcher. “These a——s, they always get away,” Zimmerman said on the call. Zimmerman, who had a concealed weapons permit, was armed.

The two then got into a struggle. Zimmerman told police he had lost sight of Martin, and that Martin circled back and attacked him as he walked back to his truck. Prosecutors say he tracked down Martin and started the fight.

Zimmerman told police Martin punched him in the nose, knocking him down, and then got on top of him and began banging Zimmerman’s head on the sidewalk. Photos taken after the fight show Zimmerman with a broken nose, bruises and bloody cuts on the back of his head. He said that when Martin spotted his gun holstered around his waist under his clothes, he said, “You are going to die tonight.” Zimmerman said he grabbed the gun first and fired. Martin died at the scene.

Given the low visibility on the dark, rainy night of the shooting, few residents of the Retreat at Twin Lakes were able to give investigators a good description of what happened, and several offered conflicting accounts of who was on top of whom during the struggle.

But 911 calls made by neighbors captured cries for help during the fight and then the gunshot. Martin’s parents say the cries for help were from their son, while Zimmerman’s father has testified they were from his son. Voice-recognition experts could play an important role in helping jurors decide who was screaming, provided they are allowed to testify. O’Mara had raised questions about whether such prosecution experts would mislead jurors and Judge Nelson has yet to rule.

For the past year, Zimmerman has been free on $1 million bond and living in seclusion.

It’s not clear whether he will take the stand, but he has already testified in pretrial hearings.

Prosecutors have refused to comment about the case outside the courtroom. Areas near the courthouse have been designated for expected protests.

“We want to make sure this trial is tried in a courtroom and not outside a courtroom,” lead prosecutor Bernie de la Rionda said.

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