Philip Markoff, the 22-year-old accused Craigslist killer of model Julissa Brisman, may seem like the least likely of killers. But when all the facts are known, Markoff's story (if he is convicted) will start to make sense. Granted, he's a reasonably affable medical student without a criminal record a• but Scott Peterson was a friendly fellow and seemingly good neighbor before murdering his wife Laci and their unborn son, Conner. Dr. Richard Sharpe, the Harvard dermatologist (and cross-dresser, it turns out) was a respected physician prior to shooting his wife to death in front of their children. Dr. Jonathan Kappler, a California anesthesiologist who murdered my friend and colleague Paul Mendelson back in 1990, had worked for decades as an anesthesiologist prior to accelerating to 60 mph in his car and intentionally mowing Paul down as he jogged.

Psychiatric instability is often invisible until we look for it, in retrospect, after a terrible event triggers the inquiry. But the evidence of that instability and the causes of it are never absent once we start digging.

In the case of Philip Markoff, we could start excavating the roots of his violence by looking at his gambling habit. If it is true that he owed gambling debts that motivated him to rob women-for-hire in hotel rooms, then he may have been someone deeply moved by the wheels of fate - by risk or ruin being determined by the alchemy of skill and the luck of the draw at a poker table. In my experience treating gamblers, their connection to fate often comes from having little or no control over their lives as much younger people. Sometimes, that adds up to having had parents who could have cared less about their feelings or desires. Sometimes, it adds up to not knowing when the next beating was going to come. And sometimes, it adds up to too many sudden losses.

But it always adds up. When someone shoots a woman, then calmly walks to his car sending off text messages, he is unmoved by the cruelest roulette life can serve up. Somewhere deep inside him, he is used to destruction because he has been destroyed. He is without feelings because he has tried desperately to wall off his own - whether fear or grief or rage.

If I were with Markoff right now, I'd want to know why gambling spoke to him. Why was Foxwoods the kind of place he felt at home? Why was it the place he reportedly planned to marry his fiance?

Markoff also allegedly preyed upon women. He didn't pistol whip drug dealers and make off with their cash. Maybe, if he's guilty, he's had it in for women. Maybe he harbors deep feelings that his life was "stolen" from him with the dissolution of his parents' marriage and its aftermath. Maybe he thinks they're all prostitutes when it really comes down to it. Maybe he thinks they're dangerous enough to him emotionally a• or even physically a• that they need to be tied up. We don't know - yet. We never know, until we ask the relevant psychological questions.

I've been a forensic psychiatrist now for many years. And I've learned one thing for sure_ No killer comes out of the blue. No child is born into this world evil. Every act of destructiveness can be explained. And no one, not even a medical student whose fiance loves him very much, is ultimately much of a mystery once you decide to burrow beneath the surface.

Dr. Keith Ablow is a psychiatry correspondent for FOX News Channel and a New York Times bestselling author. His newest book, "Living the Truth: Transform Your Life through the Power of Insight and Honesty" has launched a new self-help movement. Check out Dr. Ablow's website at

livingthetruth.com

or e-mail him at

info@keithablow.com

.

Dr. Keith Ablow is a psychiatrist and member of the Fox News Medical A-Team.