Both apply. Some things are hardwired from birth, some things are learned behaviours. One can dramatically affect the other. Any study of a human’s psychology must interrogate both aspects to get an accurate reading.
Edit: On Bundy, his extreme psychopathy was something he was born with, as is the case with most, if not all, serial killers. He displayed psychopathic tendencies from a very early age. His grandfather was a volent man, so that probably contributed to Bundy's outlook on the world. Mind you, that's what Bundy says, and anything he ever said has to be taken with a pinch of salt.