(CBS) --Trayvon Martin was alive for one to ten minutes after George Zimmerman shot the teen in the chest, and was still able to feel pain before he died, a medical examiner who conducted an autopsy on the teen testified Friday.
Dr. Shiping Bao, an associate medical examiner, said the bullet pierced Martin's heart. "The bullet went straight, directly from the front to the back," Bao said. "His heart beat until there was no blood left."
In court Friday, jurors saw photos including Trayvon Martin's hoodie with a bullet hole and images of the body bag Trayvon Martin's body was in when it arrived at the medical examiner's office.
Tracy Martin, Martin's father, was in court for the graphic testimony.
Bao said he ruled the manner of death as a homicide after conducting the autopsy on Feb. 27, 2012. At the time of the autopsy, Bao said Martin hadn't yet been identified, but Martin's father identified him the following day. Testifying in court Friday morning, Bao said there was "zero" chance that Martin could have survived the wound and that he was suffering for some time before his death.
"My opinion is he was still alive, still in pain, still in suffering," Bao said.
When defense attorney Don West objected, saying the comment wasn't "a relevant issue," Bao interjected, "It's relevant."
Prosecutor Bernie de la Rionda questioned Bao about the period of time following the gunshot when Bao said Martin was still alive.
"Are you saying his brain is still technically alive?" de la Rionda asked.
"Yes," Bao answered.
"He can still feel pain, in other words?"
Again, Bao responded affirmatively. He said he believed Martin likely would not have been able to move following the gunshot.
Bao noted small abrasions to Martin's left hand that another medical examiner who reviewed photos of Martin and Zimmerman testified could have been caused by Martin striking someone.
Bao told de la Rionda the injuries could have happened several hours before the altercation, during the altercation, or after the gunshot.
Responding to questioning from West, Bao said he didn't remember how Martin's clothing had been packaged. West has said that Martin's clothing was packaged wet in plastic bags, and a DNA analyst who testified this week said he detected a strong odor when he opened the bag that contained the hoodie Martin was wearing.
West asked Bao if packaging wet clothing in plastic bags was "inappropriate and a violation of protocol."
"If anybody do that, he'll be gone the next day," Bao said. "He'll be fired. It's a very basic concept to use to use paper bags instead of plastic."
West's cross-examination of Bao drew repeated reminders from the judge for only one person to speak at a time, as the medical examiner frequently interrupted questions.
Bao was still on the stand late Friday morning when the court recessed for lunch. His testimony followed the mother and brother of Trayvon Martin, who testified they recognized their son's voice as the screaming in the background of a crucial 911 call.
Court was due to resume at 1 p.m.