PANAMA CITY, Fla. — A Florida teen who collapsed during a confrontation with boot camp guards died of organ failure after they repeatedly used ammonia capsules to try to revive him, a doctor testified Thursday.

The encounter, which occurred on Martin Lee Anderson's first day at the Bay County Boot Camp, aggravated his pre-existing condition of sickle-cell trait, leading to his death, forensic pathologist Thomas Andrew said. (VIDEO)

Drill instructors Henry Dickens, Charles Enfinger, Patrick Garrett, Raymond Hauck, Charles Helms Jr., Henry McFadden Jr., Joseph Walsh and nurse Kristin Schmidt each face up to 30 years in prison if convicted of aggravated manslaughter of a person under 18.

A 25-minute surveillance video of the altercation, which the jury viewed Thursday, shows the guards covering the teen's mouth and waving ammonia capsules in his face on three separate occasions, once for as long as five minutes, while Anderson appears to pass in and out of consciousness.

The eight defendants, ages 30 to 60, say that Anderson provoked the encounter by refusing to participate in a 1.5 mile mandatory run to gauge his fitness level. The footage, which offered a glimpse into the rigid environment of the paramilitary-style rehabilitation program, showed Anderson stopping twice during the run before guards took him to the ground and used ammonia capsules when they were unable to get him on his feet.

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Andrew, a forensic consultant who is also New Hampshire's chief medical examiner, said the ammonia capsules were the "tipping point" leading to Anderson's eventual "neurological collapse."

Calling the guards' use of the ammonia excessive and "inappropriate," Andrew said the intoxicating effects of the chemical were heightened by the fact that the guards covered the teen's mouth while administering it.

However, it was everything combined, including the stress of the encounter and the physical exertion of the run, that aggravated Anderson's sickle-cell condition, hampering the flow of oxygen in his blood, he said.

"But for these defendants' actions, would Martin Anderson have died?" assistant state attorney Scott Harmon said.

"I would have to say no," Andrew said.

Andrew said that, had the guards given Anderson the opportunity to recover from the run, his death might have been prevented.

The primary dispute in the case is over the cause of Anderson's death. Two autopsies conducted after Anderson's parents took him off life support on Jan. 6, 2006, came to different conclusions about whether his death was unavoidable because of his condition or was the result of the defendants' actions.

Defense attorneys claim that the guards' use of force was not excessive and that Anderson would have died regardless of their actions because of his condition.

During cross-examination, Andrew conceded that the outcome could have been different if the teen did not have sickle-cell trait.

The witness agreed with defense lawyer James White that he was playing the role of "Monday morning quarterback" by offering a perspective on the circumstances that the defendants did not have at the time of the incident.

For example, none of the defendants knew that Anderson had sickle-cell trait. Defense lawyers claim their ignorance of his condition rendered them unable to properly respond to Anderson, whom they say should not have been at the boot camp in the first place because of his condition.

On Thursday, jurors learned that not even Anderson's pediatrician, who had treated him since he was 6 years old, knew he had sickle-cell trait.

Dr. Samir Ebeid said that he never tested Anderson for sickle-cell trait, nor did his mother ever inform him of it during the boy's life.

Although Anderson had the rare yet typically benign condition, which affects approximately eight percent of the African-American population, Ebeid said, he was a healthy boy who never exhibited problems beyond the occasional skin rash.

An assistant principal at Emerald Bay Academy testified that Anderson was a good athlete who often played basketball without difficulty in the Florida heat, dressed in his uniform of khaki pants and polo shirt.

On the morning Anderson was transferred from a juvenile detention center to the boot camp, he also appeared to be healthy and in decent spirits, according to one of his jailers.

Former guard Richard Koester testified that he even noticed Anderson smiling before he left for boot camp the morning of Jan. 5, 2006.

"He had the same demeanor that most of them do when they're fixing to go off to boot camp," said Koester. "Many have that false bravado with a little bit of nervousness underneath."

Testimony resumes Friday.