Autopsy: David Carradine Died by Asphyxiation

Cross-Dressing Linked

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 cases, patients had made previous 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 his 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 a hallmark 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.

The Associated Press contributed to this report.