Prosecutors in the George Zimmerman trial called the medical examiner who performed Trayvon Martin's autopsy to the witness stand Friday.

Medical examiner Shiping Bao is a graduate of Anhui Medical University in China. He said he performed the autopsy report in Volusia County on Feb. 27, 2012 when Trayvon had not been identified.

"The cause of death is gunshot wounds on chest," Bao said. He later said Trayvon "did not stand a chance."

During testimony, Bao said he was relying on his seven pages of notes and the six pages of the autopsy report to testify. He said he did not remember the specifics of the autopsy.

"I told you before, I tell you right now," Bao said. "I do not remember anything."

While he did not want attorneys to see his notes, Judge Debra Nelson ordered him to do so. The copies would later be destroyed, Nelson said.

Bao told Prosecutor Bernie de la Rionda that he thought Trayvon lived for one to 10 minutes after he was shot. Defense attorney Don West said that in a previous statement Bao said he thought Trayvon lived for one to three minutes after he was shot.

Bao first opined that THC levels in Trayvon's blood could not have affected his behavior. During his Friday testimony, Bao said he changed his mind six days ago, after doing research and talking to a biologist.

"Marijuana could have no effect or some effect," Bao said.

Nelson said she was standing by her decision that the jury would not have access to the toxicology report or to Bao's ambivalent opinions on the effect of THC.

During cross examination, West brought up the toxicology report twice. Every time he did, De la Rionda objected and Nelson reminded him to abide by the court's decision.

Bao also said that his opinion was that the gunshot immobilized Trayvon, but that there was only one person in this world who knew that.