Martin Lee Anderson was sent to the Bay County Sheriff's Office boot camp on Jan. 5 for a probation violation. A surveillance video showed guards kicking and punching him after he collapsed while exercising on his first day at the camp, and he died at a hospital early the next day.
The security video shows as many as nine guards kneeing, hitting and dragging Anderson around the exercise yard. The sheriff's office has said the guards were trying to get Anderson to participate after he became uncooperative.
The county sheriff's office, which runs the camp, said Anderson was restrained after he became uncooperative. But the camp also admitted that mistakes were made, CBS News correspondent Jim Acosta reports.
After seeing the videotape, the boy's parents agreed to have his body exhumed. They asked Baden, Dr. Michael Baden, a noted pathologist who had reviewed medical evidence in the slaying of civil rights leaders Medgar Evers and the Rev. Martin Luther King Jr., to observe the new autopsy.
The Bay County medical examiner initially concluded the teenager died from complications of sickle cell trait, a usually benign blood disorder.
The new autopsy was conducted Monday by Hillsborough County Medical Examiner Vernard Adams. Baden said it was clear the teen did not die from sickle cell trait, or from any other natural causes.
"My opinion is that he died because of what you see in the videotape," said Baden, referring to the surveillance video.
Baden said it will be several weeks before Adams can determine the exact cause of death because tissue samples must be analyzed and other evidence considered.
Pam Bondi, a spokeswoman for Hillsborough County State Attorney Mark Ober, confirmed Baden's assertion but would not elaborate, saying it will be months before the investigation is complete. Ober was appointed by Gov. Jeb Bush to investigate the case.
Anderson's mother, Gina Jones, said she was glad the truth was out.
"But I already knew what the truth was. Now the truth is out, and I want justice," she said.
No guards have been arrested or fired but the camp has been closed.
The U.S. Attorney's office in Tallahassee and the Justice Department's Civil Rights Division also have opened investigations.
Dr. Charles Siebert, who made that initial ruling after Anderson's death Jan. 6, was present at the second autopsy and may end up changing his ruling, Baden said Tuesday.
"I think he made a mistake," Baden said.
Siebert did not immediately return a call seeking comment Tuesday.
Ober has declined to discuss the investigation. No guards had been arrested or fired by Tuesday, but the camp, operated by the Bay County Sheriff's Office, has been closed. The U.S. Attorney's office in Tallahassee and the U.S. Justice Department's Civil Rights Division also have opened an investigation into Anderson's death.
Civil rights leaders who rallied to support Anderson's parents said they hoped the case would lead to reforms.
"He was a microcosm of many young Andersons sitting in boot camps and detention centers across the state of Florida," said Sevell C. Brown, state president of the Southern Christian Leadership Conference.