In this video, we're looking at the case of the first serial killer in human history. Are you familiar with the Spanish cave, "Sima de Los Huesos"? While there are far more interesting caves, there's something very unusual about this one. Back in 2013, human remains were discovered in this Pit of Bones, even though its depth is 43 feet or 13 meters. After some research, it became clear that the cave was the burial place for the victims of the very first killer in human history. What was the reason for this murder? How was it done? Let's have a look!