They are born with a psychopathic gene that is only activated through repeated abuse growing up. Its easier for them because they have no empathy so it is easier to stick multiple amounts of people without thinking it. Through empty heartednees they use killing as a way to get back at the world for wrong doing them in some cases, serial killers put on a face however to trick there prey into thinking they are good average individuals. For cannibals however who also happen to kill eat there victims to feel empowered that'd why they eat them is to feel more powerful than there prey, its not only for the sick addiction of it. They kill not only for the addiction but mostly for the empowerment. Ted Bundy felt betrayed from his mother for lying to him his whole life in telling him she was his sister, most of his victims that he killed look like his mother, there is even that link between the killer and the killed there's a correlation between the two.

I would definitely say the way they are raised. Unless they have a mental illness such as schizophrenia. Most children follow their parents foot steps, or the environment around them. People are taught to hate, if you teach a person to respect and love other that's what they will do. If you teach them to hate that's what they will do. I am not really good with words but I hope you understand what I'm trying to say, if not I'm sorry I tried :)

Nelson Mandela

“No one is born hating another person because of the color of his skin, or his background, or his religion. People must learn to hate, and if they can learn to hate, they can be taught to love, for love comes more naturally to the human heart than its opposite.”

If this is how you do "research" for your "college essay" you are going to be out of college and back on the McD's fry line quicker than you can say "Rah, rah, siss boom bah."

There has been a "violence" gene (don't know the actual name) but not everyone who inherits it becomes a serial killer, or even kills once, or even is actively violent. They are born that way, but the environment, how they are raised, can balance it.

Sometimes it's a bad gene, otherwise it's how they're raised.

See Wikipedia: SERIAL KILLERS, an excellent site with data to back it all up.

most serial killers are mentally ill, they might not have been born that way and it might not be anything to do with how they where brought up

I would say serial killers are affected by their surroundings