"David was pretty strange," she said. "He would like to get tied up. He would tie himself up and I would walk in and see him and say, 'Oh my God, David, you got to be kidding me -- and I would (turn around and) walk out. I would leave him to his own devices."
Jensen, who was divorced from Carradine in 1997, added, "He liked to be tied up. And he could tie himself up ... He spent days planning a different feature. He would go to a hardware store and buy the stuff."
"It was never sexual," she said, noting that Carradine liked bondage but never choked himself.
His fourth wife, Marina Anderson, told ABCNews.com that her claims in her 2003 divorce papers that he practiced "deviant" and "dangerous" sex behavior, including incest, were true.
Carradine had been married five times and has five daughters and two sons.
But according to Dr. Martin Kafka, clinical associate professor of psychiatry at McLean Hospital in Belmont, Mass., all that has been reported on Carradine's body is consistent with auto-erotic asphyxia.
"[It] is often associated with sexual masochism - sexual arousal to bondage/restraints, pain and humiliation, such as bound hands and testicles, and transvestic fetishism, such as women's clothing and undergarments and dildoes if they were present," said Kafka.
As for how one reaches orgasm with hands tied behind the back, he noted that anoxia -- severe oxygen deprivation -- alone can be associated with orgasm.
But, added, who has nothing to do with the Carradine investigation, "I do not know if that is fact or fiction."
According to forensic psychiatrist Stephen Hucker of the University of Toronto, auto-erotic asphyxia is also associated with mood disorders, and in 60 percent of the cases, patients had previously made attempts to take their lives.
Though Carradine's ex-wife Anderson said he was "always happy when he was working," he reportedly suffered from bouts of depression and had written about suicide.
He also abused alcohol, according to Anderson, who was credited with sobering up the actor for the role in "Kill Bill."
Even though the family has said Carradine was happy at the time of his death, working on the movie "Stretch," experts say many who practice this deadly sex act have other mental issues.
Admiring the act itself is also hallmarks of the deadly practice.
"Sometimes a mirror will have been placed strategically near the body to allow the subject to view himself as he performs his ritual or a camera may have been set up so that the person may photograph or videotape himself," according to Hucker. "Others will create an entire environment that relates to some special fantasy and may involve, for example, the creation of a torture chamber or other obviously sadomasochistic theme."
Besides mirrors, sexual paraphernalia can include self-photography, bondage, hoods, blindfolds, enemas, electrical stimulation and beating of self or by a partner.
Because auto-erotic asphyxia is so "heavily stigmatized, by its very nature practitioners lead a hidden life," said Kafka.
"That [Carradine] had a substance abuse problem or had suicidal thoughts is not all that surprising," he told ABCNews.com. "That would make sense."
Even after the investigation of Carradine's death is complete, it still may be difficult to determine if it was an accident, a suicide or even a murder.
"It's hard to know their intention because we can't ask them," Kafka said.