Even the most plain, factual description of Andrew Conley’s murder of his kid brother is chillingly disturbing:

The teenager told police he choked his brother while they were wrestling until the boy passed out. He said he then dragged his brother into the kitchen, put on gloves and continued strangling him for at least 20 minutes.
He then put wrapped the boy’s head in two plastic bags. A coroner testified that Conner may have still been alive for minutes or hours after that point, Humphrey noted, but the bags helped suffocate him, and Conley repeatedly banged the boy’s head on the ground before loading him in the trunk of his car to make sure he was dead.

He then went along with his day, compounding the horror with his casual behavior.
As a parent, especially, the violation of warm images of home and basic trust in familial bonds leaves only one word capable of describing the act: Evil. Questions of insanity and premeditation are tangled, because the monster had previously expressed admiration for a fictional television serial killer but found the experience surreal and felt outside himself and unable to stop. In that regard, the case puts the lie to insanity as an excuse for the inexcusable; the perpetrator must be considered insane by definition, and to consider that as mitigation is to negate our ability to deal appropriately with… again… evil.
Clearly, the killer was not well. Surely, the images and plots that gave form to his illness help to spread the blame to the parents who allowed them to infect their home, to the people and industry that produces them, and to the broad society that creates a market for destructive filth. If that society is to be substantively free, the slow, dispersed culmination of evil must be tolerated until it sharpens in the hands of a depraved person and a criminal act. But is that clinical assessment sufficient?
Columnist Ron Rosenbaum recently touched on similar thoughts for First Things. Writing about the West Cumbria killer dubbed “Psycho-Cabbie”:

… one could see Derrick “simmering with rage and paranoia” and perhaps even the dread low self-esteem, too. But we are all simmering to some extent. And yet: Murdering his twin in cold blood and then driving over to his solicitor’s house and shotgunning him in bed, too? Are these bad choices psychogenically determined, organically inevitable? Crimes just waiting to happen if we’d had a proper brain scan to warn us? Or are they evil? Can we utterly eliminate the fact that he had a choice, that he made a choice, and that it was an evil choice? Or do we just look at his brain scan posthumously for the real trigger? And what do we make of the nine further killings that morning, and of the dozen or so attempts that left several critically wounded? …
… [After his initial, pre-motivated murders] virtually every time he saw anyone—a person with whom he did not have any kind of psychogenic, emotional, legal relationship—he chose evil, more and further evil, until he totaled a dozen dead victims and then shot himself. He was in a world of utter freedom offered by the fact that he could not become any more morally or legally culpable than he already was. He was free to be as evil as he wanted to be. He could have shot himself after the first three, but he chose to blast open the faces of a dozen or so more, nine of them fatally.

The problem that Rosenbaum doesn’t entirely resolve is that externalizing evil — whether as a series of biological or psychological triggers or as a demonic force — tends to complicate our sense of how to handle those who become its instruments. “If we are not free to choose evil,” he concludes, “we are not free to refuse it,” and the court psychologist might argue that, as a matter of law, society cannot fully punish those who were not free to resist the impulse toward their crimes.
At least with the notion of evil as a spiritual force, we can blame the perpetrator for “leaving the door open.” With modern concepts of agency, even that degree of culpability is not as available. Who opened the door by which evil approached Indiana’s fratricidal teen? And to the degree that evil takes the form of illness (psychological, biological, or both), blame seems less a matter of the active opening of a door than of the passive failure to close it.
Which is to say that all of the tools that have accrued to the modern intellect remain unable to address, and may in fact exacerbate our comprehension of, the evil to which our species has proven prone. Leave it thus: He who submits to evil must be punished for his acts in the body, even while redemption remains possible, spiritually. Those who cleared the path for evil should contemplate long and seriously their culpability. And the rest of us should make it our life’s work to counter evil with good.