With the disclaimer that I’m not a professional, probably both, and without contradiction, question only being if the first change or the first behaviour occurs first.
As for culpability, that’s an interesting subject for me as well, since I’m an academic scholar of criminal trial law. This also has a more personal angle: if sociopaths truly have acquired the condition as a result of something they didn’t choose (or even chose at some point but can’t choose to get out of without aid, it generally being believed that the extent of aid they can receive is limited), then we can’t load them with guilt for all the suffering we have personally experienced due to their condition. Certainly we should apply collective responsibility, since they’re individual persons, not a hive mind.
At least NPD can originate often from either very turbulent childhoods or being spoiled beyond measure by parents, none of which is really the child’s fault (children’s culpability being reduced in general anyway, in proportion to justified expectations of them). Other people with psychopathic personalities have been victims of horrible crimes. It isn’t as clear as choosing to be a jerk and getting it burnt into one’s brain as a result of the habit.
In the end, it may be that someone whom we treated like a criminal and like someone who had practically abdicated his humanity, was in reality a badly hurt child that never got a chance to grow into a normal person (which is comparable to turning insane as a result of torture).
And we definitely should avoid scapegoating them at any rate.
(This, however, is not justify anybody who actually chose to become a jerk. Or to say that we shouldn’t protect ourselves from abuse. Or that we can give in to urges that we are capable of resisting.)