The 72-year-old actor's body wasat Bangkok's Swissotel Nai Lert Park Hotel. Police initially said they suspected suicide, though Carradine's associates had questioned that theory.
Police Lt. Gen. Worapong Chewprecha told reporters that Carradine was found with a rope "tied around his penis 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 due to an orgasm."
Thai police completed an autopsy on Carradine Friday but so far have not released the results.
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 he did not elaborate.
Police Lt. Teerapop Luanseng had said on Thursday that Carradine's body was found "naked, hanging in a closet," and that police at the time suspected suicide.
But actor Michael Madsen, a longtime Carradine friend, said The Early Show Friday the suicide theory "doesn't make sense."
"I could never have imagined anybody like David, (who) was so full of life and so happy and working," Madsen said. "You figure somebody might do something like that when they're unemployed or destitute. He was working hard and having a good time."
"I spoke to his wife this morning," Madsen added, "and she really wants everybody to know that David was not suicidal. Certainly, I would have known about something like that. Depression wasn't really a part of his personality. Whatever causes people to have that emotion, he seems to have -- seemed to have gotten over it.
One of Carradine's managers, Tiffany Smith, of Binder & Associates, also 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."
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.
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.
Carradine, a martial arts practitioner himself, was best known for the U.S. TV series "Kung Fu," which aired from 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 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 - Vol. 1." In that film, one of Bill's former assassins (Uma Thurman) begins a vengeful rampage against her old associates, including Bill.