Wikipedia: Delfina and María de Jesús González (known as “Las Poquianchis”) were two sisters from the Mexican state of Guanajuato, located some 200 miles north of Mexico City. During the 1950s through the mid-1960s, the sisters ran Rancho El Ángel, called the “bordello from hell”.
The police picked up a woman named Josefina Gutiérrez, a procuress, on suspicion of kidnapping young girls in the Guanajuato area, and during questioning, she implicated the two sisters. Police officers searched the sisters’ property and found the bodies of 11 men, 80 women and several fetuses, a total of over 91. Investigations revealed the scheme was that they would recruit prostitutes through help-wanted ads; though the ads would state the girls would become maids for the two sisters. Many of the girls were force fed heroin or cocaine. Then when the prostitutes became too ill, damaged by repeated sexual activity, lost their looks, or stopped pleasing the customers, they killed them.
They would also kill customers who showed up with large amounts of cash. When asked for an explanation for the deaths, one of the sisters reportedly said, “The food didn’t agree with them.” Tried in 1964, the González sisters were each sentenced to 40 years in prison. In prison, Delfina died due to an accident, and Maria finished her sentence and dropped out of sight after her release. Although they are often cited as the killers, there were two other sisters who helped in their crimes, Carmen and Maria Luisa. Carmen died in jail due to cancer; Maria Luisa went mad because she feared that she would be killed by angry protesters. The sisters were the subject of the 1977 book Las Muertas by Mexican author Jorge Ibargüengoitia.