Police Thursday released an incident report that gave new clues that support Zimmerman.
When police arrived and found the body, they also found Zimmerman bleeding from the nose and back of his head, according to the report. Also, the back of his shirt was wet and had grass clippings on it, as if he'd been on his back on the ground.
And an officer overheard Zimmerman complain, " 'I was yelling for someone to help me but no one would help me,' " according to the report.
One of the things on which police are focusing is the background noise in a 911 call, the chief said.
"You can hear the struggle and the gunshot," he said.
Police want to enhance the background noise to better hear what went on, he said.
Detectives should complete their investigation next week at the latest, the chief said, and will let the state attorney's office decide whether to file criminal charges.
At the family's news conference in Orlando, lawyers for Martin's family accused Zimmerman of racial profiling.
One of the family's attorneys, Benjamin Crump of Tallahassee, called Zimmerman a "loose cannon" and accused him of shooting Martin in "cold blood".
Zimmerman had spotted Martin in his gated community about 7:15 p.m. and called Sanford police on a non-emergency number, saying he'd just seen a suspicious person, both sides agreed.
That call then ended and police dispatched an officer. Before he arrived, however, the department got several other 911 calls, people complaining about two men fighting and a gunshot.
At the news conference, Crump and Orlando attorney Natalie Jackson said there was nothing suspicious about the 17-year-old. There was no reason for Zimmerman to follow him.
Martin was an invited guest, visiting his father's fiancée and her family for a few days, they said. He had visited there before, and it was a community with black and minority residents.
