Seminole County in Florida is home to around 313,000 people.

In order to try George Zimmerman for the murder of Trayvon Martin, prosecution and defence lawyers only need to find 10 citizens there who have not already made up their minds about the case. But it is proving to be difficult.

Is Zimmerman a racist vigilante who stalked an unarmed teenager, then shot him dead? Or was Martin an aspiring thug who confronted a man on neighbourhood watch, smashed his head against the pavement and reached for his gun? These competing narratives have been debated so intensely by the American media that this has become one of the most closely-watched trials in years, fraught with issues of race and the legitimate – or not – use of lethal force.

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Of the 500 people summoned to the Seminole County Courthouse, 30 will be selected for a second round of questioning, before six jurors and four reserves are chosen. Judge Debra Nelson has ruled that they will be isolated for the duration of the trial, with limited access to television and the internet.

The first week of jury selection demonstrated how few people have yet to form an opinion about what happened on the night of February 26, 2012, as Martin walked back to his father's girlfriend's house in a neighbourhood called the Retreat at Twin Lakes, in the Seminole city of Sanford. He was carrying a can of iced tea and a bag of Skittles.

"Murder is murder, even in self-defence. Still doesn't make it right," said one potential juror.

Another said: "I believe every American has the right to defend themselves. The more people armed the better."

Some expressed a fear there will be reprisals against the jury after the verdict, whatever it is. "There are enough crazy people that it makes me nervous," said one woman.

"I think I'm going to walk out of here with a bulls-eye on my back," suggested a man.

Local television stations are broadcasting the process without showing the faces of potential jurors. Judge Nelson indicated that their names will be kept secret for "a period of time" after the trial.

Much of the key evidence has already been made public – anyone can listen to Zimmerman's call to the police. "We've had some break-ins in my neighbourhood," he told the operator, "and there's a real suspicious guy- these assholes always get away."

Despite being told that a police car was on its way, he pursued Martin on foot. "He's running? Are you following him?" asked the police dispatcher. "We don't need you to do that."

In emergency calls made a few minutes later by residents of the housing estate, someone can be heard screaming for help. Martin's family say it is Trayvon's voice. Robert Zimmerman insists that he can hear his brother shouting.

Although no-one witnessed the start of the confrontation, several people had a view of its fatal conclusion, but they cannot agree on what they saw: Was Martin on top of Zimmerman, or vice versa?

Zimmerman's supporters note the broken nose, two black eyes and facial lacerations listed on his medical examination. His detractors wonder why it showed no evidence of head trauma, if Martin had pounded his head into the concrete, and why Zimmerman's DNA was not found under Martin's fingernails if he was responsible for the scratches.

Shootings, mostly black-on-black, are the leading cause of death among young African-American men. In the six weeks after he was killed, before Zimmerman was charged with second-degree murder, Martin became a martyr – the hooded sweatshirt he was wearing when he died a protest symbol against racial disparities in the justice system.

Basketball stars LeBron James and Dwayne Wade took to the court with "RIP Trayvon Martin" and "We want justice" written on their shoes. Congressman Bobby Rush was kicked out of the House of Representatives for wearing a hoodie. The Reverend Al Sharpton led a march on the city of Sanford.

"It really brings to light the question of how the lives of black men and boys are valued," said Dr Niaz Kasravi, national criminal justice director of the National Association for the Advancement of Coloured People (NAACP). "We know that there are many Trayvons out there."

When Barack Obama observed, "if I had a son, he'd look like Trayvon", conservative radio host Rush Limbaugh complained that the president was "trying to fan the flames of this rather than cool it down".

The case also drew attention to "stand your ground" laws, popular with gun owners, that create a broad definition of the right to self-defence. Although Zimmerman elected not to seek a hearing under the statute, it influenced the police decision not to arrest him.

On informing Tracy Martin that his son had been killed, the officer said the gunman was not in custody because he claimed to have been defending himself. "That was the first thing that came out of the detective's mouth – that [Zimmerman] had a squeaky-clean record, a licence to carry a weapon and is studying criminal justice," Martin recalled.

Representative Dennis Baxley, a Republican, was responsible for introducing the law. He said: "Ultimately this case is going to be about what happened in those final moments: was it a 'kill or be killed' situation or not.

"There will be close calls near the boundary in some of these situations, but I think overall - if you empower people to stop violent acts, they can, they will and they have."

Opponents say there is evidence of racial bias in the law's application. The Tampa Bay Times found that 73% of people who used a "stand your ground" defence after killing an African-American were successful, compared with 59% in cases where the victim was white.

"A lot of people of colour happen to be at the wrong end of that gun," said Kasravi. "It's giving people carte blanche to shoot first and ask questions later."

Zimmerman was only charged after Florida's governor, Rick Scott, appointed a special prosecutor to investigate the case.

Norton Bonaparte, Sanford's city manager, said: "I think the fact Trayvon Martin was shot and killed and George Zimmerman was not immediately arrested struck a chord in some parts of America as another example of blacks not getting equal justice.

"It also uncovered some deep distrust issues between members of the African-American community in Sanford and the police department, and we're dealing with that."

In June 2012, Cecil Smith became the city's first black chief of police, after Bill Lee was sacked for his handling of the Martin case.

Sanford is a racially mixed city with a per capita income of $21,000, surrounded by wealthy, predominantly white Seminole County. In 1946, African-American baseball icon Jackie Robinson was driven out of town by whites. Five years later, voting rights activist Harry Tyson Moore and his wife were murdered by the Ku Klux Klan.

"That was the times. We've changed since then," said Bonaparte. "Certainly Sanford is a southern Florida city, and there have been issues, but if there's a sense that it is a racially divided city then that is misleading and inaccurate."

The Retreat at Twin Lakes is a gated community, built just before the property market imploded in 2007. Houses are worth roughly half what they were, and there has been a significant number of foreclosures, leading to high turnover. In the year before the shooting, police were called to the estate more than 300 times, often by Zimmerman himself, complaining about potholes, unruly children, stray dogs and open garage doors.

Authorities are aware that the verdict could provoke an "emotional response" and have taken steps to dampen any trouble. Pastor Paul Benjamin, a leader of the Love Sanford Project, founded to "keep the peace, bring spiritual, economic and social renewal" to the city, told me that the initial failure to arrest Zimmerman "stirred up latent resentment that is always brewing, like a volcano".

Zimmerman's defence team lost a key battle when Judge Nelson ruled that it will not be able to mention Martin's marijuana use or school suspensions in its opening statement. For months, it has been leaking information to sympathetic media outlets: a text message in which Martin asks a friend whether he has a gun, tweets written under the name "no_limit_nigga", a video that Martin shot of two homeless men fighting over a bicycle.

Martin was suspended from school three times in the months before his death. One suspension was for writing graffiti, another for truancy, a third when a bag containing traces of marijuana was found in his backpack. The Martin family has said this was nothing more than normal adolescent behaviour, characterising the leaks as "a desperate and pathetic attempt by the defence to pollute and sway the jury pool".

The photographs used in reports about the case are telling. In liberal media outlets, Martin is a smiling kid with a birthday cake, in a suit or an American football uniform. On conservative websites, he is a glowering would-be "gangsta" with a roll of banknotes, gold grills on his teeth, giving the camera a one-fingered salute.

Fox News pundit Geraldo Rivera caused an outcry when he suggested that "the hoodie is as much responsible for Trayvon Martin's death as George Zimmerman was". Last week, in a web chat for the network, former NYPD detective Harry Houck opined that "Trayvon Martin would be alive today if he didn't have a street attitude".

Kasravi, of the NAACP, said the Martin case is "the first time since 9/11 that the nation is paying attention to the risks of racial profiling," adding that the deaths of young African-American men in questionable circumstances often go unreported. Just last month, a judge dismissed a manslaughter charge against Richard Haste, a New York police officer who shot and killed an unarmed teenager, Ramarley Graham, in the bathroom of his flat.

Many conservatives believe Zimmerman should never have been charged. His legal defence has been paid for by more than $300,000 in online donations.

The verdict will hinge on whether jurors believe his claim that, after initially running away, Martin took him by surprise, attacking him with such ferocity that Zimmerman believed his life to be in danger.

The prosecution's star witness will be a girlfriend of Martin's who was on the phone with him when the altercation occurred. In her statement to investigators, she said that Trayvon told her he was being followed by a "crazy and creepy" guy and shouted "get off, get off" shortly before the line went dead.

Some legal analysts believe that the decision to charge Zimmerman with second degree murder may backfire on prosecutors, as it requires them to prove beyond a reasonable doubt that he had a "depraved mind" when he shot Martin.

In Sanford, community leaders just hope that whatever the verdict, the trial will be seen to be fair. "We pray that the truth will be made known," Benjamin said. "And we pray that justice will be served."