Police: Trayvon Martin beat man before being shot TRAYVON MARTIN SHOOTING

WASHINGTON, DC - MARCH 26: Members of the National Black United Front hold a Trayvon Martin Solidarity Rally outside the U.S. Department of Justice March 26, 2012 in Washington, DC. Trayvon Martin, a 17-year-old Florida high school student, was shot and killed, in Sanford, Florida on February 26. (Photo by Win McNamee/Getty Images) less WASHINGTON, DC - MARCH 26: Members of the National Black United Front hold a Trayvon Martin Solidarity Rally outside the U.S. Department of Justice March 26, 2012 in Washington, DC. Trayvon Martin, a ... more Photo: Win McNamee, Getty Images Photo: Win McNamee, Getty Images Image 1 of / 12 Caption Close Police: Trayvon Martin beat man before being shot 1 / 12 Back to Gallery

Sanford, Fla. --

With a single punch, Trayvon Martin decked George Zimmerman, the neighborhood watch volunteer who eventually shot to death the unarmed 17-year-old, then climbed on top of Zimmerman and slammed his head into the sidewalk several times, leaving him bloody and battered, according to an account released Monday by authorities.

That is the account Zimmerman gave police, and much of it has been corroborated by witnesses, authorities say.

Zimmerman has not spoken publicly about what happened, but that night, Feb. 26, and in later meetings he described and re-enacted for police what he says happened.

Police disclosed to the Orlando Sentinel that there is about a one-minute gap, after Zimmerman called police and before he fatally shot Martin, during which police say they're not sure what happened.

In Zimmerman's version of events, he had stopped following Martin and had turned around and was walking back to his SUV when Martin approached him from behind. The two exchanged words, then Martin punched him in the nose, sending him to the ground, and began beating him.

Then, Zimmerman says, he 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 was unequivocal that it was Zimmerman who was crying for help.

Zimmerman, who claims self defense, 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. He was given first aid by paramedics but refused to go to the hospital.

New background information on Martin emerged Monday. He had been suspended from Dr. Michael M. Krop Senior High School three times, most recently for possession of an empty bag with marijuana residue and a "marijuana pipe," according to a school's report obtained by the Miami Herald.

Civil rights leaders and thousands 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, who was gunned down while walking back from a 7-Eleven with nothing more sinister than a package of Skittles and can of Arizona iced tea.

Supporters have held rallies in Sanford, Miami, New York and Tallahassee, calling the case a tragic miscarriage of injustice.

Zimmerman has gone into hiding. A fringe group, the New Black Panthers, have offered a $10,000 reward for his capture.

The Department of Justice last week opened a civil rights investigation into what happened, and Florida Gov. Rick Scott appointed a special prosecutor.

McClatchy Newspapers contributed to this report.