George Zimmerman, the neighborhood watch crime captain who shot dead 17-year-old Trayvon Martin, originally told police in a written statement that Martin knocked him down with a punch to the nose, repeatedly slammed his head on the ground and tried to take his gun, a police source told ABC News.

Zimmerman had claimed he had called police about Martin, whom he found suspicious, then went back to his car when Martin attacked him, punching him.

The new information is the most complete version yet of what Zimmerman claims happened on the night of Feb. 26 when he shot and killed the teenager.

In addition, an eyewitness, 13-year-old Austin Brown, told police he saw a man fitting Zimmerman's description lying on the grass moaning and crying for help just seconds before he heard the gunshot that killed Martin.

The initial police report noted that Zimmerman was bleeding from the back of the head and nose, and after medical attention it was decided that he was in good enough condition to travel in a police cruiser to the Sanford, Fla., police station for questioning. He was not arrested.

Martin's girlfriend had said in a recording obtained exclusively by ABC News that she heard Martin ask Zimmerman "why are your following me, and then the man asked, what are you doing around here." She then heard a scuffle break out and the line went dead.

Phone records obtained by ABC News show that the girl, who is 16 and asked to remain anonymous, called Martin at 7:12 p.m., five minutes before police arrived, and remained on the phone with Martin until moments before he was shot.

ABC News has also learned that Martin was staying in Sanford at the time because he'd been suspended from Krop High School in Miami after school officials found him with a baggy that they suspected contained marijuana. He was staying at his father's fiance's house in Sanford.

Family spokesperson Ryan Julison confirmed to ABC News that Martin was suspended for an "empty baggy that had contained pot."

"It's irrelevant to what happened on Feb. 26, does not change material facts of the situation, specifically that had George Zimmerman not left his vehicle and heeded the police dispatcher's guidance, we wouldn't be here today," Julison said.

During Zimmerman's call to 911, the dispatcher asked him if he was following the teen. When Zimmerman replied that he was, the dispatcher said, "We don't need you to do that."

Martin's mother, Sybrina Fulton, said at a news conference today, "All I've got to say is they killed my son, and now they're trying to kill his reputation."

The new information threatens to heighten tensions in the emotionally charged case. Sanford's Mayor Jeff Triplett told ABC News that "the city today is a tinder box."

"This city is a glass house, and making matters worse the civic center has a lot of glass," he said referring to a town hall meeting slated for 5 p.m. where family and residents will be airing grievances about the Martin shooting.

In addition, the Rev. Al Sharpton said today that he and other protesters intend to "occupy" Sanford on Easter weekend and pray that the city arrests Zimmerman.

The details of Zimmerman's early account of the confrontation could complicate pressing charges against him, which one veteran prosecutor has already said could be difficult.

"The stand-your-ground law is one portion of justifiable use of deadly force," veteran State Attorney Angela Corey told ABC News. "And what that means is that the state must go forward and be able to prove it's case beyond a reasonable doubt… So it makes the case in general more difficult than a normal criminal case."

Zimmerman shot Martin dead the night of Feb. 26 after following him for several minutes. Zimmerman told police Martin looked suspicious because he was wearing a hoodie, and when he confronted him the two fought -- ultimately resulting in a single bullet in Martin's chest.

Trayvon Martin Case: Timeline of Events

Zimmerman claimed self defense and this weekend the lawyer counseling him, Craig Sonner, told ABC News that he was likely to invoke Florida's controversial stand-your-ground law in his defense.

The law affords people enormous leeway to use deadly force if they feel their life is seriously endangered. Sonner said Zimmerman felt "one of them was going to die that night," when he pulled the trigger.

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