The ancient egyptians, Who in turn taught Pythagoras, Which in turn influenced plato and aristotle etc, All believed in a human soul. They also believed in reincarnation. Aristotle had the most to say about it, Stating that a person can not decide against what they are currently deciding to do.
As you cannot make a "square circle", The definition of a soul posits on the fact that decision making would be impossible if we were merely the sum of our parts, Or were multiple organisms somehow perfectly working in cohesion with each other. This is because in order to get everything working together, You'd have to wait until coordination is possible, But then again, What decides to wait for the coordination? You'd have to have enough coordination to even decide to wait for coordination which in itself IS coordination, So it makes no sense to say that souls do not exist. There must be some central decision maker, A single observer to control the body. Otherwise this "coordination" would be impossible, And would be subject to infighting, Much like a two headed snake.
Which leads us to the fact that the reason evil people commit evil acts is because they LACK a central decision making capability, And they don't actually observe anything. They are merely anatomical robots caught in limbo between the living and the dead. They lack a soul, And therefore are incapable of comprehending right and wrong. They are merely impulsive, Out of control abominations. Those who murder and rape simply need to be disposed of and thought of as little more than the fertilizer we should convert them into.
I was taught that evil people have souls just like everyone else but their souls are damaged and twisted by merciless acts that need to be touched by mercy. The word mercy comes from the Latin Root word misericordiae which means to tend to or cure a soul damaged by evil and misery. In case you didn't know, There are stories where evil people become good. Wernher von Braun was a Nazi scientist but he jumped shipped and joined the U. S. During the Cold War. Saint Paul went from murdering people for religion to dying for the same religion. Some enemy soldiers converted into good people after being confronted by prisoners. Therefore, Evil people have souls that are weighed down by trauma and wrongdoing and only the proper act of mercy and restore them and make them a good person.