Trayvon Martin was returning from a trip to the convenience store carrying only a bag of Skittles and a bottle of iced tea when a neighbourhood vigilante approached him in a gated Florida community.
Moments later, the unarmed black teenager was lying fatally injured in the grass, in a shooting that has sparked growing outrage and accusations of institutional racism.
Nearly a month after the incident, the gunman – 28-year-old George Zimmerman – has not been arrested, let alone charged, shielded by a Florida law protecting gun owners.
As details of Trayvon's death on 26 February have been pieced together by US news outlets, public outrage has steadily mounted, and late on Monday, the US Justice Department agreed to open an investigation into the death.
The federal department's civil rights division, along with the FBI, will attempt to establish how detectives concluded that a slight, 17-year-old boy represented a mortal threat to his stocky killer, who had taken to mounting night-time patrols of a gated community in Sandford, Florida.
Their independent review comes after a petition calling for Mr Zimmerman's prosecution attracted more than 550,000 signatures and was endorsed by a slew of left-leaning celebrities, including Spike Lee, Wyclef Jean, and Mia Farrow. Demonstrations are being held across Florida's university campuses while civil rights leader Al Sharpton was due to arrive in Sandford, a commuter city north of Orlando, last night, to discuss the case's increasingly ugly racial overtones.
Mr Zimmerman, originally described by police as a white male, has long styled himself as a "neighbourhood watch co-ordinator". He spotted Trayvon while patrolling the gated community in an SUV. The teen, who was staying at the nearby home of his father's girlfriend, had visited a local convenience store during half-time of a televised basketball game and was walking home. Since it was raining, he wore a hooded top.
"This guy looks like he's up to no good, or he's on drugs or something," Mr Zimmerman told 911. "These assholes, they always get away." Then, against the advice of an operator, decided to confront Trayvon.
In the ensuing altercation, several neighbours heard cries for help, followed by the sound of the fatal gunshot. Police swiftly arrived on the scene, but declined to make an arrest, after Mr Zimmerman claimed that he acted in self-defence.
That decision is now the subject of widespread derision, along with claims that white police officers either botched their investigation or deliberately moulded it to dovetail with the suspect's version of events. Several witnesses have, for example, said they heard a boy calling for help, and were shocked to hear the police describe those cries as Mr Zimmerman's. Tapes of the 911 call have suggested that he acted aggressively. Forensics indicate that Trayvon was initially approached from behind.
Trayvon's parents are doggedly campaigning for a proper investigation into the shooting. His mother, Sybrina Fulton, appeared on television on Monday to allege that her son was killed because Mr Zimmerman was: "reacting to the colour of his skin".
The victim's girlfriend revealed yesterday that she had been speaking on the phone to him immediately before the attack. "Why are you following me?" she heard him ask Mr Zimmerman. "What are you doing here?" came the reply. After that, his phone was apparently thrown to the ground.
As well as inflaming race-relations, the killing has shed uncomfortable light on a "Stand Your Ground" law introduced by Republicans in Florida in 2005 with the intention of protecting gun owners. It allows a crime victim who is "in fear of great bodily injury" to use deadly force in public.
Caught on tape: 'This guy looks like he's up to no good'
The anger that followed the shooting of Trayvon Martin three weeks ago exploded after the release of the 911 tapes of the incident earlier this week. They reveal that the alleged gunman, George Zimmerman, had followed the teenage victim despite being advised not to by the operator.
Mr Zimmerman can be heard on the tape calling police to report a suspicious character in the gated community in Sanford, Florida, where he lived. "This guy looks like he's up to no good, or he's on drugs or something," he tells the dispatcher. "These a**holes, they always get away," he adds. Mr Zimmerman tells the operator that he is following Trayvon, after which the operator tells him not to do so.
A second 911 call, this time from a neighbour who witnessed a struggle between the two men, could also prove crucial to any future investigation.
The neighbour says she can hear "someone screaming outside."
"I don't know why. I think they're yelling help but I don't know," she says. The sound of a struggle can be heard, followed by gunshots.
After hearing the tapes, Trayvon's father, Martin, said that he was "positive" that it is his son's voice that can be heard screaming for help in the neighbours' calls.
"It's heart-wrenching, because those actually were my son's last words," he said.