Czech police say 15-year-old Alena Skrivankova told 10-year-old Jitka Svehlova's parents that the pair were going to a nearby wood "to play."
Instead, the teen allegedly tied the young girl to a tree and used an ax to slice her fingers. Police say the 10-year-old broke free mid-attack and ran home.
According to the Mirror, Skrivankova was still at the crime scene when police arrived:
A police spokesman said: "Somehow the younger girl managed to escape and her horrified parents called the police.
"When officers arrived at the scene they found the older girl sitting on the ground with the axe in one hand and the severed fingers in the other.
"This is a deeply disturbing case."
Skrivankova apparently told responding officers she attacked her friend as a sacrifice to Satan. She is being held pending a psychiatric assessment.