AMSTETTEN, Austria, May 2 (UPI) -- The Austrian man who imprisoned his daughter for 24 years in a cellar and fathered her seven children also sadistically abused his wife, a relative said.

The sister-in-law of Josef Fritzl, who confessed to holding his daughter Elisabeth in the cellar for decades, said Fritzl enjoyed humiliating his wife, 68-year-old Rosemarie, during social gatherings at the couple's home in Amstetten, The Independent reported Friday.

Police say Fritzl, 73, imprisoned his daughter Elisabeth and repeatedly sexually abused her, fathering her seven children, one of whom died as an infant. Three of the children remained with her, never seeing daylight until their release this week. Three children lived with the Fritzls.

"You could feel (the children's) constant fear of punishment," she said in an interview published by the Austrian newspaper Osterreich and reprinted in British newspaper.

"The worst things were his crude, dirty jokes, which he used to laugh loudly about. This was embarrassing for everyone, because we all knew they hadn't had sex with each other for years," the woman, identified as Christine R., told The Independent.

A second man Fritzl introduced as a plumber also apparently visited the cellar, which was off-limits to others, the woman said.