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George Zimmerman Trial: Experts say self-defense claim could be tough to refute in Trayvon Martin killing

George Zimmerman arrives in court at the Seminole County courthouse for a hearing Dec. 11, 2012, in Sanford, Fla.
George Zimmerman arrives at the Seminole County courthouse for a hearing Dec. 11, 2012, in Sanford, Fla. His second-degree murder case is scheduled to go to trial June 10. AP Photo

(CBS) -- Among the strongest evidence in George Zimmerman's defense may be George Zimmerman himself, several experts say - in part, because it may prove difficult for prosecutors to refute his claim that he killed Trayvon Martin in self-defense.

PICTURES: George Zimmerman faces murder charge

READ: Trayvon Martin Shooting: A timeline of events

Zimmerman, a former neighborhood watch captain, is charged with second-degree murder in the shooting death of the teen during an altercation in February 2012 in Sanford, Fla. His case  is set to go to trial Monday, June 10.

"There's only two people who know exactly what happened, and one of them is no longer alive," said Florida criminal defense attorney Brian Tannebaum, president of the Florida Association of Bar Defense Lawyers and past president of the Florida Association of Criminal Defense Lawyers. "It's a hard burden when Zimmerman is going to say, 'Listen, I was in fear, I got into a fight with this kid, I didn't know him, I didn't know what he was going to do.' What is out there to dispute what he's saying? That's the difficult part."

Watch key videos from the George Zimmerman/Trayvon Martin case on Crimesider

Jose Baez, lead defense attorney for Casey Anthony, who was acquitted of murder, said he doesn't believe the prosecution can prove beyond a reasonable doubt that Zimmerman's story isn't true.

"The state is going to have a hard time refuting the claim of self defense- that's where the case can easily be won by the defense," Baez said. "The state not only has to put forward their evidence, they have to exclude every reasonable hypothesis of innocence and do so beyond a reasonable doubt - I don't think they can."

The defense will likely point to evidence including the photos of Zimmerman bleeding from the head following the altercation to corroborate his story, Tannebaum said. Though it's not clear whether the 29-year-old will take the stand in his defense, experts say they believe it's likely.

"Unless the state makes the argument that [Zimmerman's injuries] were self-inflicted, they clearly occurred through some kind of altercation," Tannebaum said."If Zimmerman is going to testify and say Trayvon Martin assaulted me and I was in fear for my life, that would be a big piece of evidence."

What exactly happened in the Retreat at Twin Lakes gated townhome community on the night of Feb. 26, 2012 - and who started the altercation - will certainly be at issue throughout the trial. But it's less clear whether either side will attempt to paint a picture of Martin's personality for the jury.

Zimmerman's defense team recently released a series of photos in which Martin, 17, is seen blowing smoke and making obscene gestures, as well as text messages in which he talks about fighting, smoking marijuana, being suspended from school and being kicked out of his mother's home.

Though Seminole County Circuit Judge Debra Nelson ruled at a May 28 pre-trial hearing that jurors would not hear details of Martin's alleged past drug use and fighting or suspension from school during opening statements, the defense may still be able to introduce some of the evidence at trial if they prove to her its relevance.

At the hearing, Zimmerman's attorney Mark O'Mara told the judge that Martin's alleged marijuana use and past fighting were central to the self-defense argument.

"We have a lot of evidence that marijuana use had something to do with the event," O'Mara said at the hearing. "It could have affected his behavior."

The defense may push to use the evidence in an attempt to demonstrate to jurors that Zimmerman had reason to feel his life was in danger, Tannebaum said.

"An unarmed black kid in the area is not a legal reason to fear for your life," Tannebaum said. "They will want to get in every piece of evidence they can that will cause the jury to believe that George Zimmerman was in fear."

Also at issue is the significance of several key 911 calls in which a state audio expert claims Martin is heard in the background saying, "I'm begging you." Other experts have said the shouts were a mix of Martin and Zimmerman.

The judge is scheduled to rule at a June 6 hearing on whether the state expert used scientifically acceptable techniques, the Orlando Sentinel reports.

In another recording that some have speculated could be damaging for the defense, Zimmerman calls 911 to report a suspicious person, and tells the dispatcher he is following the teen.

Baez, however, says the fact that Zimmerman himself called 911 may actually lend weight to his self-defense claim.

"You don't call the police if you're trying to murder someone," Baez said.

Complete coverage of the George Zimmerman/Trayvon Martin case on Crimesider

Watch key videos from the George Zimmerman/Trayvon Martin case on Crimesider