Police have been reluctant to provided details about 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 Trayvon walking through his gated community.
Trayvon was visiting his father's fiancée, 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 Trayvon as black, acting strangely and perhaps on drugs.
Zimmerman got out of his SUV to follow Trayvon on foot. When a dispatch employee 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 Trayvon and was walking back to his SUV when Trayvon approached him from the left rear, and they exchanged words.
Trayvon asked Zimmerman if he had a problem. Zimmerman said no and reached for his cell phone, he told police.
Trayvon then said, "Well, you do now" or something similar and punched Zimmerman in the nose.
Zimmerman fell to the ground and Trayvon got on top of him and began slamming his head into the sidewalk, he told police.
Zimmerman began yelling for help.
Several witnesses heard those cries, and there's been a dispute about from whom they came: Zimmerman or Trayvon.
Lawyers for Trayvon's family say it was Trayvon, but police say their evidence indicates it was Zimmerman.
One witnesses, who has since talked to local television news reporters, told police he saw Zimmerman on the ground with Trayvon on top, pounding him and was unequivocal that it was Zimmerman who was crying for help.
Zimmerman then shot Trayvon 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.
