A 13-year-old Brazilian girl was arrested for murdering her eight months pregnant older sister and cutting out the baby from her womb to give it to another woman, police said Tuesday.

On Oct.18, the victim, identified as 23-year-old Fabiana Santana, had gone on a night out with her son, seven-year-old Gustavo, her 13-year-old unidentified sister and her sister’s 15-year-old friend. When they did not return home, their relatives filed a missing complaint.

Three days later, Santana’s body was found buried in a vacant plot of land. Her face was disfigured and there were several stab wounds on her body. Her son’s body was found floating in a lake, meters away from where Santana was buried. The newborn was found alive in the care of the 15-year-old boy at his home. The boy’s mother, identified as 35-year-old Catia Rabelo, who was on the run, was detained for questioning during which she confessed to inciting the 13-year-old to commit the crimes.

The 13-year-old teen was taken into custody. During interrogation, she confessed to killing her sister and her son.

“This is a crime that has shocked even the most seasoned police officers because there is evidence it was premeditated. The teenage suspect has admitted to killing her sister and her seven-year-old nephew. And told us that she threw Gustavo, who couldn’t swim, into the nearby lake then stoned him until he drowned,” police said.

The teen, however, made allegations against the victim and a family member.

“The girl made a claim that she committed the crimes out of revenge because she was sexually abused by her sister’s husband and ill-treated by Fabiana who didn’t believe her stories,” police said.

However, investigations revealed that the teen intended to give the newborn to Rabelo who had been faking a pregnancy. Rabelo wanted “a child to prove it so her boyfriend would marry her.” Rabelo’s son also helped her carry out the plot.

While Rabelo was charged with masterminding the plan, the two teens were charged with double homicide and were being held in a youth custody center. Meanwhile, an autopsy revealed that the victim may have been alive when the baby was cut from her womb. The newborn was reported to be in good health and was under observation at a hospital.

handcuffs
This image shows a pair of handcuffs at the Commissariat de Police Nationale (National Police Station) in Alfortville, France, Nov. 21, 2016. THOMAS SAMSON/AFP/Getty Images