Michael Brown, the killed teenager, on his Facebook page.

NYT: Twenty miles away from the home of Darren Wilson, the police officer who killed the teenager Michael Brown, in Ferguson, the Brown family said it was no closer to understanding the circumstances that led an unarmed 18-year-old to be shot to death by a police officer in the middle of the day.

The family insisted that Mr. Brown had no history of violence or aggression. He had no adult arrest record, according to the police, who said they could not speak to whether he had been arrested as a juvenile.

Administrators at the chaotic public high school he attended, one of the worst in the state, said he was quiet, shy and a little awkward, hardly one of the “trouble kids,” of which there were plenty.

“You’d sit in a house with him, watching TV and hanging out, and you’d forget he was there,” said Tim Sneed, 23, a close friend and neighbor. “He had not one enemy. I’ve never heard of him getting in one fight.”

Mr. Brown was still a teenager: He smoked marijuana with friends in the neighborhood, they recalled, and drank cans of Bud Light with them when he ducked away from the watchful eyes of his family.

Last Saturday, the day Mr. Brown died, dawned sunny and warm, around 80 degrees, a typically hot August day in Missouri. With a friend, Dorian Johnson, Mr. Brown set out to West Florissant, wearing a white T-shirt, khaki shorts and a red Cardinals cap.

About 10 minutes before noon, they entered Ferguson Market and Liquor, a run-down store with shelves lined with potato chips, Boone’s Farm wine and tequila.

Mr. Brown, who was 6-foot-4, had an intimidating appearance — his friends nicknamed him Bodyguard because he was so tall.

According to the surveillance video, Mr. Brown approached the counter, leaned over and grabbed a handful of Swisher Sweets, then turned for the door. He pushed a clerk who tried to stop him, then left the store.

At 11:51 a.m., the police said, someone called 911 to report a robbery.

Several blocks later, at 12:01 p.m., they were confronted by Officer Wilson while they continued down Canfield, a quiet street that curves gently as it weaves through apartment buildings and one-story brick houses.

They were stopped not because the police were looking for a robbery suspect, Chief Jackson said Friday, but “because they were walking down the street blocking traffic.”

Devin Stone, 28, a friend of Mr. Brown’s, was home in his apartment at the time, across the street from the place where the men were confronted by the police.

Sitting outside his building, Mr. Stone said he was jolted by the sound of two gunshots, followed by several more in rapid succession. The second series of shots “sounded automatic,” he said. “They let it rip.”

Mr. Stone ran outside and saw two police officers, both white men, standing near Mr. Brown, who was lying on his stomach, his arms at his sides, blood seeping from his head. Another neighbor, a woman who identified herself as a nurse, was begging the officers to let her perform CPR.

They refused, Mr. Stone said.