With a single punch, Trayvon Martin decked the neighborhood watch volunteer who eventually shot to death the unarmed 17-year-old, then climbed on top of George Zimmerman and slammed his head into the sidewalk several times, leaving him bloody and battered, authorities told The Orlando Sentinel.
That is the account Zimmerman gave police, and much of it has been corroborated by witnesses, authorities said.
Zimmerman has not spoken publicly about what happened, but that night, Feb. 26, and in later meetings police said he described and re-enacted for them what he says happened.
In Zimmerman's version of events, according to police, he had turned around and was walking back to his SUV when Martin approached him from behind, the two exchanged words and Martin punched him in the nose, sending him to the ground, and began beating him.
Zimmerman told police he shot the teenager in self-defense.
Civil rights leaders and millions of others have demanded Zimmerman's arrest, calling Martin a victim of racial profiling and Zimmerman a vigilante.
Martin was an unarmed black teenager who had committed no crime, they say, and who was gunned down while walking back from a 7-Eleven with nothing more than a package of Skittles and a can of Arizona iced tea.
Supporters have held rallies in Sanford, Miami, New York and Tallahassee, calling the case a miscarriage of injustice.
Police have been reluctant to provided details of all their evidence, but this is what they've disclosed to the Sentinel:
Zimmerman was on his way to the grocery store when he spotted Martin walking through his gated community.
Martin was visiting his father's fiancee, who lived there. He had been suspended from school in Miami after being found with an empty marijuana baggie. Miami schools have a zero-tolerance policy for drug possession.
Zimmerman called police and reported a suspicious person, describing Martin as black, acting strangely and perhaps on drugs.
Zimmerman got out of his SUV to follow Martin on foot. When a dispatcher asked Zimmerman if he was following the 17-year-old, Zimmerman said yes. The dispatcher told Zimmerman he did not need to do that.
There is about a one-minute gap during which police say they're not sure what happened.
Zimmerman told them he lost sight of Martin and was walking back to his SUV when Martin approached him on his left from behind, and they exchanged words, according to police.
Martin asked Zimmerman if he had a problem. Zimmerman said no and reached for his cellphone, he told police.
Martin then said, "Well, you do now" or something similar and punched Zimmerman in the nose, police said.
Zimmerman fell to the ground and Martin got on top of him and began slamming his head into the sidewalk, police said he told them.
Zimmerman began yelling for help.
Several witnesses heard those cries, and there has been a dispute about from whom they came: Zimmerman or Martin.
Lawyers for Martin's family say it was Martin, but police say their evidence indicates it was Zimmerman.
One witness, who has since talked to television news reporters, told police he saw Zimmerman on the ground with Martin on top, pounding him and was unequivocal that it was Zimmerman who was crying for help.
Zimmerman then shot Martin once in the chest from very close range, according to authorities.
When police arrived less than two minutes later, Zimmerman was bleeding from the nose, had a swollen lip and had bloody lacerations to the back of his head.
Paramedics gave him first aid, but he said no to going to the hospital. He got medical care the next day.
The U.S. Department of Justicelast week opened a civil rights investigation into the shooting, and Florida Gov. Rick Scott appointed a special prosecutor.