Fred and Rose West
“A married couple, they sexually abused, tortured, and beat their child and teenaged daughters and other women, eventually killing several of their own children, along with other women, and burying them under the patio in their own garden. Absolutely sickening. Unlike many husband-wife murderer pairs, the wife, Rose, was completely in on it and took pleasure in the murders, committing some alone while her husband was in prison, rather than just being an accomplice.
Apparently, Fred would threaten his surviving children that they would “end up under the patio like Heather” (his own daughter, who they beat to death because they didn’t like the look on her face) if they misbehaved.” — 360Saturn