Documents shed new light on Trayvon Martin killing

Updated 9:44 PM ET

(CBS/AP) ORLANDO, Fla. - Trayvon Martin was shot through the heart at close range. George Zimmerman had a broken nose, bruises and bloody cuts on the back of his head.

The lead investigator in the case wanted to charge Zimmerman with manslaughter in the weeks after the shooting but was overruled.

CBS News correspondent Mark Strassmann reports the released evidence covers 183 pages. It includes dozens of audio recordings: mostly interviews, surveillance videos, and reports about physical evidence. And it tells the story of a struggle just before the fatal shot.

The last images of Martin were from a surveillance video taken at a 7-11 store in Sanford, where the 17-year-old bought Skittles and a can of iced tea before heading back to the townhouse subdivision where he was staying with family. Twenty minutes later, he would be dead, shot fatally once in the chest by Zimmerman.

Thursday's document release includes crime scene photos, including one of Zimmerman's 9-millimeter gun, the first time it's been seen.

Yet it's still unclear what exactly happened and whether it was racially motivated.

The evidence supports Zimmerman's contention that he was being beat up when he fired the fatal shot. At the same time, it bolsters the argument of Martin's parents that Zimmerman was profiling Martin and that the whole confrontation could have been avoided if not for Zimmerman's actions.

Many of the pertinent questions remain unclear: What was in Zimmerman's mind when he began to follow Martin in the gated community where he lived? How did the confrontation between the two begin? Whose screams for help were captured on 911 calls? And why did Zimmerman feel that deadly force was warranted?

Another opportunity for answers isn't likely to come until a hearing later this year in which Zimmerman is expected to claim the shooting was justified under Florida's "stand your ground" law. Zimmerman's attorney, Mark O'Mara, didn't return a phone call seeking comment Thursday.

The evidence supporting Zimmerman's defense includes a photo showing the neighborhood watch volunteer with a bloody nose on the night of the fight. A paramedic report says Zimmerman had a 1-inch laceration on his head and forehead abrasion. (At left)

"Bleeding tenderness to his nose, and a small laceration to the back of his head. All injuries have minor bleeding," paramedic Michael Brandy wrote about Zimmerman's injuries in the report.

Whether Zimmerman was injured in the Feb. 26 altercation with Martin has been a key question. The 28-year-old has claimed self-defense and said he only fired because the unarmed teenager attacked him.

Zimmerman was not arrested for weeks because he invoked Florida's "stand your ground" law, which does not require a person to retreat in the face of a serious threat. He was released on bail and is in hiding while he awaits trial on a second-degree murder charge. He has pleaded not guilty.

Other evidence supports the contention of Martin's parents that Zimmerman was the aggressor.

The investigator who called for Zimmerman's arrest, Christopher Serino, told prosecutors that the fight could have been avoided if Zimmerman had remained in his vehicle and awaited the arrival of law enforcement. He said Zimmerman, after leaving his vehicle, could have identified himself to Martin as a concerned citizen and talked to him instead of confronting him. The report was written on March 13, nearly a month before Zimmerman's eventual arrest.

He said there is no evidence Martin was involved in any criminal activity as he walked from a convenience store to the home of his father's fiancee in the same gated community where Zimmerman lived.

The lawyer for Martin's parents seized on the investigator's recommendation.

"The police concluded that none of this would have happened if George Zimmerman hadn't gotten out of his car," said attorney Ben Crump. "If George Zimmerman hadn't gotten out of his car, they say it was completely avoidable. That is the headline."

The release of evidence did little to clear up whose voice is screaming for help in the background of several 911 calls made during the fight.

Since first hearing the calls in early March, Martin's mother, Sybrina Fulton, has been unequivocal in saying that it was her son's voice on the tapes.

But Serino wrote in a report that he played a 911 call for Martin's father, Tracy, in which the screams are heard multiple times.

"I asked Mr. Martin if the voice calling for help was that of his son," the officer wrote. "Mr. Martin, clearly emotionally impacted by the recording, quietly responded `no."'

Zimmerman's father also told investigators that it was his son yelling for help on March 19.

"That is absolutely positively George Zimmerman," Robert Zimmerman said. "He was not just yelling, he sounded like he was screaming for his life."

Investigators sent all the recordings to the FBI for analysis. They were asked to determine who was screaming, and also if Zimmerman might have used an expletive in describing Martin. Prosecutors said in their charging documents that Zimmerman said "(expletive) punks" in describing Martin as he walked in the neighborhood.

But the analyst who examined the recordings determined the sound quality is too poor to decipher what Zimmerman uttered. In regards to the screams during the altercation, there also wasn't enough clarity to determine who it is "due to extreme stress and unsuitable audio quality."

The trajectory of the bullet — straight through Martin's body — doesn't shed light on whether Zimmerman and Martin were standing or on the ground, said Larry Kobilinsky, a professor of forensic science at John Jay College of Criminal Justice in New York.

Kobilinsky added he thought the evidence diminished prosecutors' case for second-degree murder.

The case has become a national racial flashpoint because the Martin family and supporters contend Zimmerman singled Martin out because he was black. Zimmerman has a Peruvian mother and a white father.

Two acquaintances painted an unflattering picture of Zimmerman in police interviews.

A distraught woman told an investigator that she stays away from Zimmerman because he's racist and because of things he's done to her in the past, but she didn't elaborate on what happened between them.

"I don't at all know who this kid was or anything else. But I know George, and I know that he does not like black people. He would start something. He's very confrontational. It's in his blood. We'll just say that," the unidentified woman says in an audio recording.

A man whose name was deleted from the audio told investigators said he worked with Zimmerman in 2008 for a few months. It wasn't clear which company it was.

The man, who described his heritage as "Middle Eastern," said that when he first started, many employees didn't like him. Zimmerman seized on this, the employee said, and bullied him.

Zimmerman wanted to "get in" with the clique at work so he exaggerated a Middle Eastern accent when talking about the employee, the man said. The employee told investigators that Zimmerman made reference to terrorists and bombings when talking about him.

"It was so immature," said the employee, who ended up writing a letter to management about Zimmerman.

Zimmerman's parents say he wasn't racist. They say he had mentored black students and had a black relative.

The autopsy says medical examiners found THC, the psychoactive ingredient in marijuana, when they tested Martin's blood and urine. The amount described in the autopsy report is such a low level that it would have played no role in Martin's behavior, Kobilinksy said.

"This kind of level can be seen days after somebody smokes," Kobilinsky said. "If it comes up in the case, I would be surprised. It wouldn't benefit the defense, it wouldn't benefit the prosecution, and if the defense tried to bring it up, the judge would keep it out."

A police report shows the 17-year-old had been shot once in the chest and had been pronounced dead at the scene. The autopsy says the fatal shot was fired from no more than 18 inches away.

In a police interview, Zimmerman's father, Robert, described the toll the case had taken on family members who also are in hiding because of safety concerns.

"It just seems like it's an avalanche and I'm standing at the bottom of it," Robert Zimmerman said.