(CNN) -- A teenager who died at a Florida boot camp was suffocated by guards who were restraining him, a medical examiner has determined.
The teen's mother hailed the findings, saying "the truth is out," but a lawyer for one of the guards accused the examiner of giving in to political pressure.
Martin Lee Anderson, 14, died in January after he was restrained and struck by workers at the boot camp for juvenile offenders.
No charges have been filed in connection with Anderson's death.
Initial autopsy results in February had determined Anderson died from complications from sickle cell trait, which had not been previously diagnosed in the teenage athlete.
Hillsborough County Chief Medical Examiner Vernard I. Adams conducted a second autopsy after Anderson's family, other medical experts and civil rights leaders balked at the conclusion of the first examination.
"Martin Anderson's death was caused by suffocation due to actions of the guards at the boot camp," Adams wrote.
"The suffocation was caused by manual occlusion of the mouth, in concert with forced inhalation of ammonia fumes that caused spasm of the vocal cords resulting in internal blockage of the upper airway."
But an attorney for Lt. Charles Helms, one of the guards, told CNN that he was disappointed by Adams' findings.
"It appears he caved in to the pressure of the politicians," said attorney Waylon Graham. "This is going to be a battle of the coroners."
Graham said it was "a foregone conclusion" that the guards would face criminal charges and said the first medical examiner, Dr. Charles Seibert -- who has said he stands by his conclusions -- would be "our star witness."
The entire investigation, he said, is "a witch hunt."
Parents allege cover-up Anderson's parents, Robert Anderson and Gina Jones, said they were unconcerned with Seibert's position and accused him of participating in a cover-up.
"My baby was murdered in the boot camp and he tried to cover it up," Jones told reporters.
"The truth is out," she said. "I am relieved and happy today. It's a beginning. Justice needs to be served."
Anderson collapsed January 5 at the Bay County Sheriff's Office Boot Camp program in Panama City, Florida. He had complained earlier in the day, his first at the facility, of breathing difficulties while running around a track as part of the admission process.
At one point, Anderson told the officers he couldn't breathe well enough to continue running. The report said he resisted repeated attempts to get him to complete the exercise by pulling away, tensing his body, struggling and balling his fists.
Videotape of the incident showed Anderson being forced to the ground by various takedown methods, including knee strikes to his thigh, pressure points to his ear and punches to his arms.
Later, another camp staffer hit him from behind, forcing Anderson to lurch forward. A nurse stood by, and on at least one occasion she determined his vital signs were normal.
Anderson was taken away on a stretcher and died later that day.
Adams reported that the blows "did not contribute to his death."
Adams studied the video, having it enhanced by engineers at NASA. The intake process at the facility is videotaped as a matter of policy.
'Offender refused to comply with instructions' The boot camp staff prepared a report detailing the techniques used on Anderson, including holding ammonia capsules under his nose, knee strikes, a straight arm-bar takedown, bending his wrist and pouring water over his head.
To explain the use of force, one staff member wrote, "I ordered [the] offender to stop resisting and relax his arms. Offender refused to comply with those instructions."
Some experts on juvenile justice have called it excessive force. But the sheriff's office said Anderson was restrained for being "uncooperative." The family has accused the officers of murder and demanded an independent investigation.
Florida Gov. Jeb Bush assigned the case to Mark Ober, the special prosecutor in Tampa, who in turn ordered the second autopsy and appointed Adams to conduct it. Bush on Thursday said he was "disturbed" by the medical examiner's reports and considers the camp guards' actions "deplorable."
"I assure Gina Jones and Robert Anderson that the state remains committed to providing any resources State Attorney Ober deems necessary to complete this investigation as quickly as possible," he said in a written statement.
"We all have one goal, and that is to see justice is served for Martin Lee Anderson."
The state has shut down the Bay County boot camp. At the time of Anderson's death, Florida operated five boot camps for troubled children as a substitute for prison.
The Bay County Sheriff's Office said the boot camp's closure had nothing to do with Anderson's case but also said the eight people involved in the incident were not offered new jobs.
A federal probe into whether Anderson's civil rights were violated by the use of excessive force is also under way, according to the U.S. attorney's office. The investigation was requested by the boy's parents and local leaders.
Adams and Ober said they would not comment on the case beyond their respective news releases announcing the results of the autopsy.
CNN's John Zarrella and Susan Candiotti contributed to this report.
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