Lawmakers and the family of a teenager seen on videotape being kneed and struck by juvenile boot camp guards are calling for the immediate arrest and prosecution of the guards.

The Bay County Medical Examiner ruled that Martin Lee Anderson died of internal bleeding caused by a genetic blood disorder. But his family said on Friday they believe the boy died because of the 30-minute beating that took place hours before the 14-year-old died.

The US Justice Department is investigating possible civil rights violations.

Florida Gov. Jeb Bush said he did not support calls to shut down the state's military-style juvenile boot camps, calling Anderson's death "one tragic incident."

"The coroner has suggested that the death was caused by this child's unique illness ... that ... the force itself did not cause the death," he said.

Still, Bush said he is awaiting a series of recommendations from the Florida Department of Juvenile Justice about improving the training and the quality of the camps.

Some lawmakers have called on Bush to appoint an independent prosecutor.

A spokesman for Bush said earlier on Friday that the governor thought it was too early to consider appointing an independent prosecutor in the case.

"The investigation by law enforcement hasn't been completed yet," he said.

Investigation to remain active

Florida Department of Law Enforcement officials said they provided their investigative reports to the state attorney's office and to the US Attorney and that their investigation would remain active until decisions are made about criminal charges.

State Rep. Gus Barreiro, a Miami Beach Republican, said the conclusion that Anderson died of natural causes "doesn't add up." "It doesn't make sense and goes against all logic of watching what happened to this young man," he said.

State Sen. Gary Siplin, an Orlando Democrat, called for any guard who touched Anderson to be arrested.

"At the very least it's aggravated battery, at the top of the ladder it's murder," Siplin said.

Anderson, who entered the camp on January 5 because of a probation violation, complained of breathing difficulties and collapsed while doing push-ups, sit-ups and other exercises.

He died after midnight the next day at a Pensacola hospital.

On the grainy, 80-minute tape, which has no sound, as many as nine guards, can be seen wrestling Anderson to the ground and restraining him.

The boy appeared limp for most of the ordeal and never appeared to offer significant resistance.

While he lay motionless on the ground, a guard struck him several times, either on his arm or torso. At one point, a guard struck him from behind, lifting his feet off the ground.

At the beginning, as the guards are pinning him against a pole, they struck him three times with their knees.

It is not clear from the tape how hard the blows were or where they landed.

A woman in a white coat was present while Anderson was restrained and at one point used a stethoscope to check him.

Near the end of the confrontation, guards appear to become more concerned, and several run in and out of the scene. A few minutes later, emergency medical personnel take him away on a gurney.

"Martin didn't deserve this right here - at all," the boy's mother, Gina Jones, said after viewing the tape Friday at her lawyer's office in Tallahassee. "I couldn't even watch the whole tape. Me as a mom, I knew my baby was in pain and I am in pain just watching his pain."

Cell disorder present in one in 12 African-Americans

Anderson was arrested in June for stealing his grandmother's Jeep Cherokee and sent to the boot camp for violating his probation by trespassing at a school.

State police investigating the case released the tape after a lawsuit by news organisations.

The autopsy blamed his internal bleeding on sickle cell disorder, which is present in one in 12 African-Americans but does not show up in routine blood work.

There has been research - some involving recruits at military boot camps - linking the trait to sudden death after extreme exertion. Experts on sickle cell trait, however, questioned on Friday whether the disease could be definitively and entirely to blame for Anderson's death.

"There is a slight, increased risk at the extremes of human endurance, but it really takes a profound amount of exercise and dehydration," said Dr. James Eckman, director of the Comprehensive Sickle Cell Centre at Grady Health System in Atlanta and a professor at Emory University.

Research shows sudden death with heavy exertion typically happens either in extreme heat and humidity or at high altitude. Weather records show the high temperature was 68 degrees Fahrenheit (20 degrees Celsius) the day Anderson passed out.

The boot-camp concept for juveniles began in Florida in 1993 and five camps now house about 600 boys ages 14 to 18.