ALL THAT MATTERED WAS THE GUN:

That assertion of justice for all -- in Sanford and throughout the United States -- has been challenged, though, by a progression of events that began so innocently, so ordinarily: A teenage boy in a gray hooded sweatshirt leaves a 7-Eleven's neon brightness with his purchase of some candy and an iced tea, and heads back into the wet Sunday evening of Feb. 26, back to a residential complex with a forbidding gate and a comforting name.

Trayvon Martin was more than welcome there; he was expected.

With his hood up as the rain came down, Trayvon made his way to one gated community among many, the Retreat at Twin Lakes. Past a dozen storefronts, four of them vacant. Past signs and billboards shouting "Now Leasing!" and "Rent Specials!" His was a tour of a post-bust stretch of Sanford.

For more than two years now, Trayvon's father, Tracy Martin, a truck driver from Miami, had been dating Brandy Green, a juvenile detention officer in Orlando. She lived at the Retreat with her 14-year-old son, Chad, and it was not uncommon for the Martins to drive up from Miami for overnight visits.

Over six feet tall and lanky, Trayvon was interested in girls, computer games, sports and the beat of the rap and hip-hop emanating from the ear buds of his smartphone. Sleeping in Miami Dolphins bedsheets, he was all teenage boy, and more.

He called himself "Slimm" on Twitter, and used a handle, @no_limit_nigga, that echoed a song by the rappers Kane & Abel. On Facebook, he expressed interest in  airplanes and "South Park"; Bob Marley and LeBron James. On MySpace, he posted snapshots of his young life: admiring an airplane; fishing with his father; displaying a cake decorated with the words "Happy Birthday Tray."

Easygoing, with a default mood set at "chillin'," as one schoolmate, Suzannah Charles, put it. The kind of kid who made tiny cakes in an Easy-Bake Oven with his 7-year-old cousin; who spoon-fed a close uncle, Ronald Fulton, who is quadriplegic, when his nurse was unavailable; who was an integral part of a close-knit family -- raised properly, family members say, by Mr. Martin and his ex-wife, Sybrina Fulton, who works for Miami-Dade County's housing agency.

Ms. Green described him as the kind of kid who did not bring attitude into a house, and who knew how to behave respectfully in the homes of others. "He was smooth, quiet," she said. "He took care of his appearance. He had swag."

But Trayvon was a teenager, not an angel. In his last year at his high school in north Miami-Dade County, he had received three suspensions -- for tardiness, for graffiti and, most recently, for having a baggie with a trace of marijuana in his backpack.

This last suspension, for 10 days, was enough for Trayvon's father, who stayed on top of him about his whereabouts and middling grades; after all, he wanted to go to college, just like his quiet older brother, Jahvaris Fulton, 21, a student at Florida International University.

Mr. Martin said that he had taken Trayvon with him to Sanford to keep him from hanging around Miami, doing nothing, and to talk some sense into him.

These recent problems, all nonviolent, hardly reflected the essence of Trayvon Martin, his family and friends say. He was kindhearted, even-tempered and very thoughtful. That night, for example, while his father and Ms. Green were out having dinner in Orlando, Trayvon asked Chad, Ms. Green's son, if he wanted anything from the store.

Skittles, the younger boy said.

A Wary Community

The teenager with candy entered the Retreat at Twin Lakes, either passing the front gate or taking a not-so-secret shortcut. Here was an orderly cluster of 260 or so sandy-colored, two-story town houses that illustrate an all-too-familiar American tale.

According to David Johnson, the Seminole County property appraiser, the Retreat was being built just as Florida's housing bubble was about to burst. When the first units came onto the tax rolls in 2007, he said, they were selling in the vicinity of $250,000, he said. Now, "I think those units are selling for about half."

The Retreat has had a "significant number" of foreclosures, Mr. Johnson said, which have prompted investors to buy the properties at a discount and then rent them out. "A lot of activity in and out of there," he said. "Maybe you don't know the neighbor, because the one who was there before, maybe they got foreclosed on."

Adding to the uncertainty and flux was the sense among some residents that this secured community was no longer so secure. There had been burglaries; at least seven in 2011, according to police reports. Strangers had started showing up, said Frank Taaffe, 55, a marketing specialist, originally from the Bronx, who works out of his home in the Retreat. He made it clear that he was not talking about just any strangers.

"There were Trayvon-like dudes with their pants down," Mr. Taaffe said.

Last August, the homeowners association decided to create a neighborhood watch, and a Sanford police official came to the Retreat to explain the guidelines: volunteers do not possess police powers; they should not be armed; and they should be the eyes and ears for the police -- but not vigilantes.

The group chose as its neighborhood watch coordinator the very man who had invited the official to speak: a man with thinning dark hair and an average build named George Zimmerman. The next month, the newsletter for the homeowners association included a cartoon of a man peering through a magnifying glass, à la Sherlock Holmes, next to a call for help: "We have recently experienced an increased incidence of crime within the community, including three break-ins in the past month, which is why having residents committed to being members of the Neighborhood Watch and reporting suspicious activities is so important. We must send a message that we will not tolerate this in our community!"

To get involved, the newsletter said, "Call George Zimmerman."

From Virginia to Florida

Now, on this dark, wet night, the neighborhood watch coordinator for the Retreat at Twin Lakes -- armed with a licensed, slim 9-millimeter handgun that he kept in a holster tucked in his waistband -- was in his truck when he noticed a hooded figure walking through the complex.

He may have been about to go on an errand to Target, as he later told his family, but his commitment to vigilance kicked in. This, it seems, was part of who George Zimmerman was.

He, too, was from someplace else -- the second of three children raised in a red-brick home in a cul-de-sac in Manassas, Va. His father, Robert, was a magistrate judge and a veteran of the Vietnam War, and Robert's father worked in Army intelligence. His mother, Gladys, a Peruvian immigrant, worked as a deputy court clerk. They ran a disciplined household that emphasized service, responsibility and the Roman Catholic faith.

"Some kids would have said, 'That's like a prison,' " recalled George W. Hall, a retired pastor who lived across the street. "But they were so polite. They always looked after you before themselves."

George was an altar boy looked upon so favorably by the priests that he became a receptionist in the rectory. He also joined a youth education program called the Young Marines, wearing a uniform, marching in step and learning about good citizenship.

"He was very caring toward everyone," his father said. "Toward anyone who needed anything."

But George could be a character. In middle school, a black boy named Anthony Woodson stumbled over a chair while walking into a classroom, prompting a student he did not know to joke, "Do you know how to walk, or did you trip over your lip?"

From that jarring remark, a friendship was born. Mr. Woodson said that he knew that the student, George Zimmerman, meant nothing racist, mostly because of the friends sitting with him. "Two other black kids, an Asian kid and a Hispanic," recalled Mr. Woodson, 30, now a pastry chef in Virginia. His new, bilingual friend seemed comfortable in a multicultural world.

After graduating from high school in 2001, Mr. Zimmerman moved to Florida, into a home that his parents had just bought for their retirement in Lake Mary, near Sanford. He began working as an insurance agent with an uncle, but he became a mortgage broker when the real estate market started booming. According to his father, he was making at least $10,000 a month by his early 20s.

When his parents retired to Florida around 2006, Mr. Zimmerman moved into an apartment in Lake Mary with a friend. Then the housing market went bust and, according to his father, George's employer went out of business. After that, he held several jobs, including at CarMax and Target. He also talked about becoming a police officer.

He seemed to be a young man in search of a path, one who could also show flashes of violence, according to court records detailing Mr. Zimmerman's difficult summer of 2005. That July, he was arrested after pushing a state alcohol agent during a raid to root out under-age drinking at a popular college bar; the felony charge was reduced and then dropped altogether when he agreed to enter a pretrial diversion program.

About a month later, Mr. Zimmerman and a woman who identified herself as his ex-fiancée traded petitions for injunction, both claiming that the other had resorted to violence: she said he "smacked" her; he said she hit him with a baseball bat. Both injunctions were issued and they expired a year later.

Still, Mr. Zimmerman seemed to have a protective streak -- a sense of right and wrong -- that others admired. For example, Stephanie, a neighbor of the elder Zimmermans in Lake Mary and a family friend, recalled how George Zimmerman struck up a friendship with one of her sons, Douglas, who is autistic, swimming with him, taking him for car rides and letting him play with Mr. Zimmerman's dog, Princess.

"He just felt comfortable with George," she said. "For Dougie, everything was 'George, George, George.' "

Stephanie also recalled a party in early December to celebrate Mr. Zimmerman's graduation from Seminole State College (though he still needed a few more credits to receive his associate's degree). He shared his hope to be a judge someday with a small gathering that included two black teenagers whom, she was later told by Mrs. Zimmerman, George was mentoring.

It seemed in character. A 16-year-old boy named Austin, who for a long time has mowed the lawn at the Zimmerman home in Lake Mary, described George Zimmerman as a role model for younger boys, often providing advice while throwing a football around or shooting hoops.

George would stick up for a chubby boy in the neighborhood who was being bullied, recalled Austin (who, like Stephanie, asked that his last name not be used). "And if George saw bullies walking by his house, he would pull out his hose and spray them down and tell them they were wasting their time and to go and do something else."

Mr. Zimmerman was also security-minded, Austin said. "He would knock on people's doors at night and say that it was late and that 'You better close your garage door.' "

But not everyone saw Mr. Zimmerman as their protector.

A 17-year-old African-American, Teontae Amie, who lives at the Retreat, recalled that Mr. Zimmerman once wrongly accused his friend of stealing a bike. "When you see him, you think automatically that he might try something," said Teontae, who added that he kept his distance from the neighborhood watch coordinator.

George Zimmerman seems to have taken a private vow to protect and defend -- but, for some reason, he has not realized his stated desire to become a police officer. (In 2009, though, he was accepted into Seminole County's Community Law Enforcement Academy, in which students take tours of the courthouse and jail, go on ride-alongs with Sheriff's Department employees and visit a firing range.)

"I don't think it was safety that he was concerned with as much as people's rights and people's welfare," his father said. "And where he was living has a lot of problems with people coming in and burglarizing. I think he became alarmed, and he helped organize the neighborhood watch."

Police records over the last several years suggest a man who was quite familiar with 911 dispatchers; who seemed, somehow, to be always in the middle of things. In October 2003, for example, on perhaps his greatest day in civic vigilance, Mr. Zimmerman chased after and assisted in the capture of a man who had stolen two 13-inch TV/DVD players from an Albertsons.

Mostly, though, his calls were less exciting, more anticipatory. Dangerous potholes. Stray dogs. Speeding vehicles. Open garage doors. Suspicious characters. On Feb. 2, he reported seeing a black man in a black leather jacket and printed pajamas in the Retreat; nothing came of it.

This is what George Zimmerman did.

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