P1. Gruesome Murder case you've probably never heard of

The Papin sisters, who murdered their bosses in cold blood.

French sisters Léa and Christine Papin worked as live-in servants for the Lancelin family in France in 1926. Although it was reported that they acted quite odd, never talking to anyone but themselves and showing little interest in anything besides each other, according to Historic Mysteries. They did their work quickly and lived with the family for almost seven years. 

Then, one night in February 1933, Mr. Lancelin, who had been waiting for his wife at a friend's house, came home to find her and their adult daughter dead on the floor in a pool of blood. Their eyes had been gouged out and faces smashed in. The Papin sisters were locked in their room and after getting a locksmith to open the door, the police said they found the sisters lying on the bed together with a bloody hammer nearby, according to The Vintage News.

The Papin sisters immediately confessed to the crimes. While in prison, Christine became very distressed from being away from her sister and was eventually granted permission to see Léa. Reports said that the sisters seemed to be unnaturally close to each other, with some suggesting a sexual relationship, though doctors who examined the Papin sisters denied evidence of that.

A few months later, Christine suffered a mental breakdown and tried to gouge out her own eyes. After their trial, Christine was sentenced to life in prison for being the mastermind behind the murders, while Léa was eventually released from prison in 1943 and managed to get a job at a French hotel under a new identity. It is believed that she died in 1982, but that has never been confirmed.