Whether Robert Durst is found guilty of first-degree murder in the 2000 death of writer Susan Berman depends on whether prosecutors convince a jury that he shot her, execution style, after decades of friendship.

Durst's arrest follows his participation in an HBO documentary, "The Jinx: The Life and Deaths of Robert Durst" that set out to chronicle his life and the mysterious deaths that surround him.  During the shooting of the documentary Mr. Durst was recorded while still wearing a microphone, but not on camera, stating he had "killed them all."

Prosecutors have charged Mr. Durst with murder before, when his neighbor Morris Black was shot to death in 2001.  In that case, Durst admitted cutting Mr. Black into pieces and disposing of his body.  But he claimed he did that because he was panicked that he would be unfairly judged after killing Black in self-defense while the two were struggling over a gun. 

Mr. Durst’s wife Kathleen vanished in 1982, after allegedly arguing with Durst and after allegedly having told him that she wanted a divorce.  She is presumed dead.

I have neither interviewed nor treated Durst, but as a journalist and psychiatrist, I would argue there are elements of his life that suggest how his mind works.

First, it is known that Mr. Durst left California while authorities were still probing Ms. Berman’s killing.  He donned a wig, assumed an alternate identity as a mute, female botanist and rented a cheap apartment in Galveston, Texas.

Second, it is known that Mr. Durst dismembered Morris Black, put his body parts into trash bags and then threw them into the sea.

Third, it is known that Mr. Durst’s mother fell to her death when he was 7.  Her death is believed by many to be a suicide.  Durst has claimed he witnessed his mother’s fall.  His brother Douglas disputes that.  But even Douglas has been quoted as saying that the scene was something almost beyond imagination—that he and his three siblings were suddenly awakened and whisked out of the house the night the death occurred.

Let’s take the last fact, to start with.  Just imagine the unconscious mental gymnastics a boy has to attempt in order to function after his mother, young and alive that very day, inhabiting the same dwelling as he, is suddenly dead, perhaps having caused her own death.  When a 7-year-old loses a parent in such awful circumstances, it can shake his belief in the reality of anything and everything—love, friendship, the future, even his own, core identity.  And it can make a child bury the loose ends of his grief and rage very deeply.

Was Robert Durst’s mother just pretending to be alive and well hours before her death, his 7-year-old mind might have unconsciously wondered?  Was she pretending to love him, if she then left him?  Were others pretending she was dead?

What can be trusted if one’s mother can fall off a roof, to her death, while one is warm, tucked into bed, dreaming?

And what if, even worse, Robert Durst did witness the death—or believes deeply that he did?

Not everyone can do what Mr. Durst did decades later—disappear from one state, disguised as someone of the opposite gender, pretending to have no voice, living as though impoverished, in a down-and-out apartment.  But having to pretend, at 7, to comprehend a mother’s alleged suicide, then eventually go to school and play with friends, is a kind of tragic training in disappearing.

And only a person who has experience with walling off very powerful feelings—not feeling—could dismember a body as Mr. Durst did, put the remains in trash bags, then cast them adrift.

Could such a person also kill a wife, or kill a friend, or both?  What, after all, does having a wife mean to such a person?  What does having a friend mean to such a person?  Could it mean something powerful at one moment, then be utterly meaningless the next? 

If a mother’s love can disappear, can’t any emotion?  If a mother can disappear, can’t anyone?

Maybe the full, human version of Robert Durst, for all intents and purposes, disappeared at age 7, along with his mother.  Maybe that’s why he can assume an alternate identity so completely.  Maybe that’s why he can cut up a body and throw it away.  And maybe that’s why he can tell investigators that his wife—now missing for so long—simply boarded a train all those years ago, never to be seen, again. 

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