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George Zimmerman trial: Medical examiner says he changed opinion on length of time Martin lived after gunshot

Volusia and Seminole County associate medical examiner Shiping Bao MD testifies during the George Zimmerman trial in Seminole circuit court, July 5, 2013 in Sanford, Florida. Photo by Gary W. Green-Pool/Getty Images

(CBS) -- The medical examiner who testified Friday morning that Trayvon Martin was alive for one to ten minutes after the gunshot said he changed his opinion based on a recent case at his office that was similar to Martin's.

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Trayvon Martin suffered after gunshot, medical examiner says

Associate medical examiner Dr. Shiping Bao, speaking outside the presence of the jury, told defense attorney Don West that he changed his opinion about three weeks ago after reporting last fall that he believed Martin, 17, would have been alive one to three minutes after being shot by former neighborhood watch volunteer George Zimmerman.

Zimmerman, 29, is standing trial in Martin's shooting death. Zimmerman claims he shot the teen in self-defense.

Bao was speaking during a hearing called to determine whether the prosecution knew about Bao's change of opinion and failed to report it to the defense team. Bao said he didn't tell prosecutors about the change, and a judge ruled that the prosecution didn't violate rules.

In court, Bao said he doesn't "see the problem" in changing his opinion.

"If you have new information, new experiences, you read a new book, you change your opinion," Bao said. "If someone never changes opinion, you can call them mentally retarded. You never learn, right?"

West grilled Bao on when he met with prosecutors and whether he ever told them about the change. Bao said he hadn't.

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West also honed in on another finding Bao said he changed. Initially, Bao told attorneys toxicology results revealed marijuana in Trayvon Martin's system, but said the amount of the drug wouldn't have a physical, emotional or mental effect.

Bao said that after spending "hours and hours" on new research in preparing for the trial, he now believes the marijuana "could" have had an effect on Martin.

West was continuing his cross-examination of Bao with the jury in the courtroom Friday afternoon.