As time-tested a deadly sin as avarice may be, greed alone does not explain such depravity.
"You can't get any lower than how they preyed on these people," Philadelphia police spokesman Lt. Ray Evers said.
Oh, but you can.
Two forensic psychiatrists who have made careers of plumbing the depths to which criminals can go say that as horrific as this case may seem, many have been far worse.
And worse can be measured.
According to the scales of grotesque human behavior the two have analyzed, the alleged villains - Linda Ann Weston, Thomas Gregory, and Eddie Wright - appear to be only middling sociopaths.
They've got nothing on Ted Bundy, Jeffrey Dahmer, John Wayne Gacy, and Mike DeBardeleben.
"The [Philadelphia] situation was not a pure exercise in sadism," said Michael H. Stone, professor of clinical psychiatry at Columbia University and author of the 2009 book The Anatomy of Evil.
Stone has identified 22 levels of heinousness, beginning with impulsive crimes of passion like murdering a cheating spouse, to the unthinkable - plotting to rape children and bury them alive.
Starvation, he said, "is a cheap way to kill somebody. Eventually they die, and when they do, they're lighter than when you started out, so they're easier to bury." It is also a cleaner method, "as opposed to shooting them."
Although starving is painful, Stone said, it's less so than having cigarettes burned into your neck or being whipped.
The brains of psychopaths who can do these things have been studied with MRIs and often show abnormalities, Stone said.
"The connections in the frontal lobe are not adequate. From birth, some of these people are predisposed to do this stuff, even if they have not been abused or neglected."
Ted Bundy, for instance, was a serial rapist, kidnapper, and necrophiliac responsible for at least 30 murders. "No one ever laid a hand on him," Stone said. "He was simply a very cold and callous person."
