The family of the actor, who was found dead on June 4 in his Bangok hotel suite in Thailand, had hired Dr. Michael Baden of HBO's "Autopsy" series to conduct a second autopsy after Carradine's body was returned to the U.S. last month.
Thai authorities conducted one shortly after the actor's death.
"The cause of death was asphyxiation, an inability to breathe, now why that happened is still what we're working on," Baden told the news service. Dr. Baden said the cause of death meant that suicide was ruled out as a possibility.
"He didn't die of natural causes, and he didn't die of suicidal causes from the nature of the ligatures around the body, so that leaves some kind of accidental death," he said.
Some reports suggested Carradine's death may have been the result of autoerotic asphyxiation, because of how the actor's body was found in a closet with his hands tied and a rope around his neck.
According to Reuters, when asked a question about the subject, Baden did not rule it out.
A rep for Carradine's brothers had no comment on the preliminary results of the report, according to Reuters.
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