This is not speculation but fact.
So if it is "something in our brain" then it comes from what happened after we are born. So, made not born.
Nature versus Nurture is the wrong question. Both play a role, but the issue is really how to change the outcome. There are many environmental stimuli and organic brain issues that influence violent criminals. There are simply far too many comorbid influences in all emotional, behavioral and mental health issues: genetic abnormalities; hereditary influence; organic injury; physical, emotional and developmental trauma; environmental toxins; prenatal exposure to alcohol and drugs; physical, sexual and emotional abuse; neglect; lack of familial relationships (especially fathers); repeated loss; chaos; poverty; exposure to criminal behavior; lack of religion and moral instruction; a foster care system that rewards sociopathic/psychopathic behavior; and psychoactive medications dispensed indiscriminately with few empirical studies on interactions and none on adolescent use. That’s just the tip of the iceberg.
Parsing semantics makes terrific grist for academics, but the important issue is identifying such individuals and safeguarding society. Regardless of how one classifies the individual, or how you define the behavior, we do not have options to deal with these individuals until they commit violent crimes. It is almost impossible to have someone involuntarily committed and there are really no long-term facilities available. Thanks to One Flew Over the Cuckoo’s Nest, we can no longer discriminate between a depressed individual and a violent psychopath.
Adoptive and foster parents fight constantly to find solutions for their dangerous children. These children learn how to manipulate the system from the time they are children. Every interaction builds their arsenal of manipulation. Despite deadly threats, escalating violence and repeated institutional programs, these children (and eventually adults) are returned to torment their caregivers for years. Every cry for help is met with silence and blame is placed on the very ones who are trying to make a difference. Exhausted, beaten and bloody (often a literal description), their greatest fear is not for their own lives, but of hearing their child’s name on the news. That will mean that they have failed, and someone else was hurt or killed despite their efforts.
Every time you hear about the latest murder on the news, know that there are hundreds or thousands of these people sitting in a therapist’s office just biding their time and they will not be committed long-term until they offend. When an LSD-addled shrink penned his opus, Nurse Ratched entered the American lexicon as the epitome of the villainous nurse, but the fact that she influenced national policy is a national disgrace.
Violent criminals need to be removed from society permanently. We should be discussing how best to accomplish that goal, not philosophizing on the classification or treatment of psychopaths.
On the other hand, you seem to adopt the extreme position that heredity plays NO role.