But in the case of sado-masochism, Marilyn Bagley, who was told she will not be charged if she testifies against her husband Ed, is refusing to take the stand because she believes the couple did nothing wrong.

US Attorney Beth Phillips, announcing charges last month, called the case one of "the most horrific ever prosecuted in this district", British newspaper Daily Mail reported Monday.

Authorities said the woman, who has not been identified, was a mentally deficient runaway who was recruited by Ed Bagley, 43, at the age of 16 to live in his trailer.

The case came to light in early 2009, after the woman, then 23, landed in a hospital following a torture session. She had apparently been locked in a cage and subjected to electrical shocks, an indictment said.

Bagley faces 11 charges, including conspiracy, sex trafficking by force, fraud or coercion, and forced labour trafficking.The indictment describes medieval-like sexual devices being used on the woman at Bagley's mobile home. Accusations of waterboarding, suffocation and beatings are mentioned throughout, the British daily said.

However, Bagley's wife, Marilyn, said she and her husband knew the girl because she had dated their son. That relationship had ended, Bagley's wife said, but the girl wanted to come live with the couple when relations with her adoptive parents soured.

She said the girl moved in when she was 17, not 16, and never had sex with her husband until after she turned 18. "She was not a runaway," Marilyn Bagley said. "We picked her up from her adopted dad and stepmom. They were right there and everything."

Prosecutors said Ed Bagley posted videos and other images on the internet showing the young woman engaged in sexual activities.

Ed allegedly described her as his sex slave and advertised that she would perform sex acts and submit to torture for other people during encounters online or in person. He is also accused of taking cash, cigarettes, computer hard drives and even meat, to let other men come to his home and torture her.

Bagley and other defendants are also charged with transporting the woman to California in 2006 and 2007 for prostitution.

Prosecutors said Ed Bagley also forced the girl to work as an exotic dancer and threatened to punish her if she was not a top earner at the clubs where she stripped.
But another dancer at the same Missouri strip club said the woman seemed to enjoy the attention she got when she danced.

Susan Dill, Bagley's Kansas City-based attorney, told reporters recently that the indictment tells only one side of the story. She said the defence will present evidence that the woman practiced BDSM - bondage, dominance, sadism and masochism - by choice.