At the Rensselaer Polytechnic Institute's department of cognitive science, a research team explored the logic of evil by programming a computer character named "E" that "acted on" or was motivated by a definition of evil. The Rensselaer crew defined an evil person as one who decided to commit an immoral act without prompting and carry out the plan with the expectation of considerable harm. When reflecting on those deeds, the person would either find incoherent reasons for his or her actions or think the damage caused was good. (Of course, this isn't the only definition of evil. What's labeled as heinous behavior has absolutely no standard across cultures or even among different groups of people with a particular culture.)
The researchers then programmed the character to do something "evil": give a depressed boy a gun. And not just any gun, but the one that the boy's brother had killed himself with. Extremely morbid, and -- chillingly -- a real event used as a case study in the 1983 book "People of the Lie: The Hope for Healing Human Evil." Note that in reality the people who gave the gun were the kids' parents. The researchers then proceeded to ask E why it would do such a thing. It was rather straightforward: The boy wanted a gun, so E gave him the one he had.
So an almost entirely logical explanation that basically either ignores or leaves out any kind of emotional response. Is that all evil is? It certainly matches up with some of the traits of psychopathic people, a subgroup of people with antisocial personality disorder who are commonly identified by a lack of remorse or empathy or are simply emotionally blank.
A 2009 study in the Journal of Psychopathology and Behavioral Assessment of 840 cases of psychiatric patients found that "clients with psychiatric disorders who were [sic] lower verbal IQ scores were more psychopathic; patients with greater verbal intelligence were less psychopathic" [source: DeLisi et al.]. So we can't say for sure that intelligence, or at least verbal intelligence, is needed to plot and go through with an evil act -- if psychopathy is our definition of evil.
Which begs the question: How do we know what evil is?