The 72-year-old actor's body was discovered Thursday in his luxury suite at Bangkok's Swissotel Nai Lert Park Hotel. Police initially said they suspected suicide, though Carradine's associates had questioned that theory and authorities later said no suicide note was found in his room.
Police Lt. Gen. Worapong Chewprecha told reporters that Carradine was found with a rope tied around his genitals and another rope around his neck.
"The two ropes were tied together," he said. "It is unclear whether he committed suicide or not or he died of suffocation or heart failure." Another senior officer, Col. Somprasong Yenthuam, said there was also strand of rope tied around Carradine's wrist.
"The initial cause of death is likely asphyxiation, which was probably caused by the rope that was tied around his neck," said Somprasong.
Police completed an autopsy on Carradine on Friday. But Somprasong, superintendent of the Lumpini police station, which is handling the case, said results would not be ready for at least three weeks because the cause of death was unclear. He called the time lag "normal."
Dr. Nanthana Sirisap, director of Chulalongkorn Hospital's Autopsy Center, told reporters that the autopsy was conducted because of the "unusual circumstances surrounding Carradine's death," but did not elaborate.
The body was later removed from the hospital to an undisclosed location by U.S. Embassy representatives while preparations were being made for its repatriation to the United States.
Police Lt. Teerapop Luanseng had said Thursday that Carradine's body was found "naked, hanging in a closet," and that police at the time suspected suicide.
But one of Carradine's managers dismissed the theory.
"All we can say is, we know David would never have committed suicide," said Tiffany Smith of Binder & Associates, his management company. "We're just waiting for them to finish the investigation and find out what really happened. He really appreciated everything life has to give ... and that's not something David would ever do to himself."
Pornthip Rojanasunand, director of Thailand's Central Institute of Forensic Science, said Carradine may have died attempting a sex act known as auto-erotic asphyxiation — cutting off oxygen to the brain for sexual arousal.
The practice is said to result in a form of giddiness and euphoria — similar to alcohol or drug intoxication — that enhances the sexual experience.
"If you hang yourself by the neck, you don't need so much pressure to kill yourself. Those who get highly sexually aroused tend to forget this fact," said Pornthip, who is considered the country's top criminal forensics expert but who did not take part in the autopsy.
Carradine had flown to Thailand last week and began work on a film titled "Stretch" two days before his death, Smith said. He had several other projects lined up after the action film, which was being directed by Charles de Meaux.
Carradine was in good spirits when he left the U.S. for Thailand on May 29 to work on "Stretch," Smith said.
"David was excited to do it and excited to be a part of it," she said by phone from Beverly Hills.
Filming began Tuesday, she said, adding that the crew was devastated by Carradine's death and did not wish to speak publicly about it for the time being.
Monica Donati, a spokesman for the French film company MK2, which was making "Stretch," said in statement from Paris that the film crew in Bangkok was "clearly shocked" by Carradine's death but would finish shooting. Carradine only had three more days of filming left in Bangkok, she said.
Aurelio Giraudo, the hotel's general manager, said Carradine checked into the hotel May 31 and he last saw him June 3. He said Carradine chatted with staff and even played piano a few nights in the lobby as well as flute which the "guests really enjoyed."
"I was a fan. I had a very nice talk with him when he checked in," Giraudo told The Associated Press. "He was very much a person full of life. I mentioned to him that I had seen (the movie) "Crank" with my family and that was the last smile he gave me."
Giraudo said a chambermaid discovered Carradine's body, adding that she knocked and entered after there was no response. Police arrived shortly thereafter.
Somprasong said there was no evidence there was anyone else in the room at the time of Carradine's death.
Carradine, a martial arts practitioner himself, was best known for the U.S. TV series "Kung Fu," which aired in 1972-75. He played Kwai Chang Caine, an orphan who was raised by Shaolin monks and fled China after killing the emperor's nephew in retaliation for the murder of his kung fu master.
Carradine also appeared in more than 100 feature films with such directors as Martin Scorsese, Ingmar Bergman and Hal Ashby.
He returned to the top in recent years as the title character in Quentin Tarantino's two-part saga "Kill Bill."
Bill, the worldly father figure of a pack of crack assassins, was a shadowy presence in 2003's "Kill Bill." In that film, one of Bill's former assassins (Uma Thurman) begins a vengeful rampage against her old associates, including Bill.