I'm not trying to justify him, he did terrible things, but I wonder what became the catalyst. He's mentally ill, obviously, but there must be reasons for that. Here will be only my thoughts regarding this issue, based on the information provided in the canon.
The simplest thing is if he was born like this, but it doesn't look convincing, because he's not just cruel to be cruel, he has his own goals and philosophy. He believes that his actions are an incentive for personal development as a surgeon, which means that in his concept his actions are a kind of "training". He is driven by a completely unhealthy curiosity, the goal to grow.
In addition, he has his own theory of happiness, which is as follows: "happiness can be obtained in two types of situations: when despair gives way to hope as circumstances improve, and when a person looks down on another who falls into despair."
My guess is this: Cioccolata grew up in a violent and unstable environment, he was an inquisitive child who was never properly paid attention to. In addition, during his childhood in Italy there was a deep crisis, the country lived in fear that it could imprint itself on a fragile psyche. It is very possible that he was bullied by his peers because his family was a member of one party or another.
Just to survive, he developed his theory of happiness, creating the first point, finding distraction in his studies, wanting to achieve success and cherishing the hope that his parents would pay attention to him. At that moment, narcissism could begin to develop. But not finding what he wanted, he increasingly expanded the boundaries of the new, trying to find something that would be sufficient. At the same time, he began working in a nursing home, again to gain attention and praise. He was the best in his class and received praise from the mayor.
The first k!ll could have been a mistake, after all, he was 14 years old, or he was motivated by the goal of revenge, seeing in that person someone from his environment. He may have been treated harshly by his grandmother or grandfather. At that moment, the second point of his theory of happiness appeared, which became much more entrenched. From that moment on, he realized that he didn't need to get better, it was enough for him to worsen conditions for others. But because of his narcissism and desire to be better, which could have escalated from a desire to "be better for them" to "be better than them," he continued to study.
Applying for a surgeon could have several reasons, a banal desire to be a doctor, curiosity to study the human body, or an attempt to sign off on its dark impulses. Or, which seems controversial to me, he suffered moral trauma associated with doctors or medical intervention.
Ultimately, I believe that the reason for Cioccolata's cruelty was the external environment in which he grew up.The instability of the state, the brutality in the streets and at home, and the mistreatment made him just him who he is today. He drives others to despair in order to forget what he himself experienced. He makes video recordings as trophies, but perhaps also for the sake of some ballast, which, if necessary, will remind him that now the power is in his hands. This is his own kind of ritual that means something to him. He continues to improve himself, but no longer for the sake of being noticed, but so that he can no longer compare himself to that frightened boy. It's his way of dealing with trauma, unhealthy, but for him it works perfectly.
Cioccolata's case is complicated, and there must be a combination of many facts, but I have expressed just my opinion on this matter.