How do humans become murderers? what are some of the reasons that cause it?

Humans usually become murders because the Way that they were raised usually they become murderers because they have a family history that isn't so good bike say they only killed women it's most likely caused because their mother was a very bad person to them or say that they only kill boys it's because her dad was a very bad person to them

One reason is a traumatic past that caused the person to lose it. Another reason is a person could have a mental disorder, or they just plain want revenge for something. There are many reasons to how a person can become a murder.