The murder trial begins Monday for George Zimmerman, the volunteer night watchman who fatally shot an unarmed black teenager, sparking protests across the United States and claims of racial profiling.

The trial, expected to last at least a month, begins with jury selection at 9 am local time (1300 GMT) in the Seminole County Courthouse in central Florida, near where the crime took place on a rainy night in February 2012.

George Zimmerman, now 29, faces a charge of second-degree murder for killing Trayvon Martin, 17, as he walked through the gated community to the house where his father was staying with a friend.

Zimmerman, son of a white father and a Hispanic mother, has pleaded not guilty, arguing he acted in self defense when he shot Martin after confronting him.

When police arrived, the only items found in the pockets of his hoodie sweatshirt were a pack of Skittles and a bottle of iced tea.

Sanford police initially released Zimmerman after the shooting, because they said he was acting in line with so-called "stand your ground" rules, which give immunity to those who use firearms when they feel their lives are in jeopardy.

The killing riveted the United States at the time, sparking massive protests in several US cities against what many saw as a racial bias in the crime and the police response.

Martin's death drew an expression of sympathy from President Barack Obama, and sparked a debate on "stand your ground" laws in Florida and other gun-friendly states.

Zimmerman was later arrested and faces life in prison if convicted. In the end, he opted not to base his defense on the "stand your ground" law.

If he did, it would have required him to reveal much of his pre-trial strategy to prosecutors. Instead, he is mounting a traditional self-defense case.

He argues Martin attacked him and left him with a bloodied head; he has shown photos as evidence of this.

Jury selection is expected to take several days because of the case's notoriety and the difficulty of finding people who can examine the case as objectively as possible.

"I don't believe there can be someone in this city that can be open-minded enough to be a juror in this case," said paralegal Sheena Rowland, who lives in Sanford.

Nicolas Dorsten, a lawyer specializing in "stand your ground" cases, said both sides will struggle to find objective jurors.

"This case has gotten national coverage so it will be tough to find a jury that can be fair to either side, quite frankly. It is going to be one of the struggles both the state and the defense will have to come up with."

Authorities were also gearing up for protests from civil rights advocates and pro-gun groups, gathering local, state and federal security forces and erecting barricades around the courthouse.

Hundreds of media outlets will cover the trial.

Inside the courthouse, 31 seats were reserved for reporters and photographers, around six for the families of the victim and defendant, and another four to religious leaders who have helped authorities damp down the racial tensions surrounding the case.

"It a shame that such a sad incident has drawn attention to Sanford," said Ann Johnson, manager of a small downtown hotel, but she said it's been good for business.

"We have had full occupancy in the hotels and the restaurants downtown are doing very well," she said.