MIAMI — Trayvon Martin grabbed his killer’s gun just moments before he died and uttered a profanity-laced threat. In a desperate life-or-death struggle, George Zimmerman clutched Trayvon’s wrist, broke his grip on the semi-automatic firearm and shot him once in the chest.

That account appears in a new book written by Zimmerman’s best friend and confidante.

There’s just one problem: Zimmerman never said that to the police.

Now the book, Defending Our Friend: The Most Hated Man in America, and author Mark Osterman’s two television interviews have landed on the prosecution evidence list, as more versions of Zimmerman’s story emerge. A man who wrote a book calling Zimmerman “the kindest and most sincere” person will wind up in court — for the prosecution, experts agree.

“It was emotionally draining for George as he relived that awful moment when he managed to control the gun, then fired out of fear for his life,” Osterman wrote.

Osterman, U.S. air marshal who lives in a Central Florida, was among the first people Zimmerman’s wife called on Feb. 26 when she learned her husband had just shot someone. Osterman rushed to the scene that night, and accompanied his best friend every step of the way through the investigation, including his first three interrogations by Sanford police.

Osterman acknowledges that former Sanford Police Chief Bill Lee was his one-time lieutenant in the Seminole County Sheriff’s Department whom he held up as a father figure. Osterman says he was quickly recognized by cops on the scene, but insists he never coached his friend on what to tell them after the death of Trayvon, an unarmed Miami Gardens teenager.

Afraid for the Zimmermans’ safety, Osterman took the couple in from the very first night of the shooting. His 172-page book describes how Zimmerman told the story of the killing over and over again until he was physically drained. When he told it to police, Osterman said, Zimmerman threw up.

But Osterman’s account is a sharp deviation from the versions Zimmerman gave, which experts say will undoubtedly be used to try to impeach the defendant’s credibility and cast doubt on his claim of self-defense if each telling changed or was embellished.

“I desperately got both of my hands around the guy’s one wrist and took his hand off my mouth long enough for me to shout again for help,” Osterman quotes Zimmerman as saying.

“For a brief moment I had control of the wrist, but I knew when he felt the sidearm at my waist with his leg. He took his hand that was covering my nose and went for the gun, saying, “You’re gonna die now, motherf-----.’ Somehow, I broke his grip on the gun where the guy grabbed it between the rear sight and the hammer. I got the gun in my hand, raised it toward the guy’s chest and pulled the trigger.”

DNA reports released Wednesday showed there was no DNA from Trayvon on the gun.

Even as Zimmerman himself offered slight variations of where Trayvon first appeared or from what direction, none of his written or recorded interviews with police suggested a battle over the firearm. He told police that when he wriggled off the concrete onto the grass, his gun was exposed, and Trayvon reached for it.

In the version Zimmerman’s brother Robert told CNN, Trayvon said something like, “You have a piece? You die tonight.”

Osterman has declined to comment. In his book, he blames The Miami Herald for revealing his identity and compromising his position with the U.S. Department of Homeland Security. He also acknowledged that shortly after The Herald revealed his name in July, he wrote the book and went on national TV.

Defense attorney Mark O’Mara said he had never heard about a struggle for the gun. He said he read a draft of the book before it was published, but felt asking Osterman to change details would amount to witness tampering.

“He’s a friend of George’s trying to explain George to be different than the way he was perceived to be. Great — that’s a story that’s not been told,” O’Mara said. “I don’t like him talking about things George spoke to him about in confidence. I didn’t like yet another statement of George’s out there for review. It’s more of a headache.”

Although he questioned whether Osterman’s memory is accurate, O’Mara admitted that between Zimmerman’s various interviews to police, his father and brother’s accounts to the press and now Osterman’s, there are several versions of what happened that night, but he characterized the discrepancies as a surmountable obstacle. If everyone’s story was exactly the same, O’Mara said, then it would smack of a lie.

O’Mara said it took him 10 days to respond to the book draft after he received it, but when he got around to asking Osterman to scrap the book, the publishing contract had already been signed. O’Mara chalked it up to miscommunication, adding that Zimmerman has taken a court’s “no contact with witnesses” order to heart, and has not spoken to any state witnesses except his parents since he left jail on bond while he awaits trial on a charge of second-degree murder.

“We will be able to respond to the six, seven, eight different renditions of the story, how and why there are different statements,” O’Mara said. “The jury is going to believe what the jury is going to believe.”

Although Zimmerman has said Trayvon jumped him from out of nowhere, the book says he told Osterman that Trayvon first approached Zimmerman from a distance of at least 15 feet and asked him if he had a problem. In a TV interview, Osterman also claimed Zimmerman had a concussion, something that was never noted in medical records or claimed in the statements.

To explain why Zimmerman got out of his car while on the phone with police, he quotes a conversation between his friend and the dispatcher that never took place: “If you can’t see him do you still need us to send an officer? We need you to get to a place where you can see him,” he quotes the dispatcher in an exchange that is not contained on copies of the police call or transcripts widely posted on the Internet.

Trayvon’s supporters believe Osterman’s book proves that Zimmerman can’t keep his story straight because none of it is true.

“He has done George no favors by writing this book,” said attorney Natalie Jackson, who represented Trayvon’s parents in their mission to get police to make an arrest. “This book is huge. It hurts George a lot.”

Although second-hand quotes are generally inadmissible in court, Jackson said this is a type of citation that would be exempt from the hearsay rule.

“The state would be precluded from directly using any excerpts from the book, as the words on the pages are hearsay, but the Ostermans could be subpoenaed to testify against him to his detriment if Zimmerman embellished, added or changed facts in the version he gave to them,” said Miami Beach criminal-defense attorney Michael Grieco, who has been following the case. “Any inconsistencies amongst the numerous statements Zimmerman has given will be used against him and his credibility.

“Zimmerman’s credibility is the key to his affirmative defense.”