Five years ago, my closest friend Karyn was killed by her 19-year-old son. Headlines were splashed all over the newspapers, my friend’s face on every TV screen. It was unthinkable! Unbearable! I struggled to grapple with what had happened. It didn’t make any sense. I watched this kid grow up, he was a good kid who loved his mother.

My friend was like my twin sister. We had met so many years ago, and immediately became inseparable. We wore the same clothes, cut our hair to look short and spiky, we loved the same music and watched the same movies. We were a team, and together we could do anything. We dreamed up ideas for the stories and films we wanted to make, and wrote them, and eventually made them.

We had kids together eventually, and I was there when her son was born.

How could he have committed such a heinous act? I was desperate for an explanation.

My friend’s son had developed epilepsy when he was around 14. He had also engaged in various drugs at a young age, and had some issues that were not resolved. On an April morning in 2012, coming out of a seizure, he beat his mother to death with his fists. The sound of this horrific event was captured on a desperate 911 call she made. The tape captures her cries for help and the thuds of the struggle.

He was charged, sent to Rikers Island for over a year, and in 2014, through a plea deal, he was released to a private inpatient mental facility for observation and treatment.

The only time I saw him, after her death, was at Bellevue Hospital before he was sent to Rikers. I needed to see him face to face, to look into his eyes and maybe see into his soul, to try to find a clue of some sort. But by the time I got there, the narrative of the lawyer was already taking shape. “I didn’t do it, it wasn’t me,” he told me. His legal defense was that the epilepsy and medication he was taking put him in an altered state not fully conscious, and he “did not appreciate the nature or consequences of his actions at the time” (his lawyer’s words).

Several weeks after the death, another friend gave me a book to read which she thought would have some significance for me. It was Pat Barker’s novel “Border Crossing,” which really struck a nerve and affected me in a profoundly personal way. It is the story of a child psychologist who is haunted by his expert witness testimony that sent a young boy to prison for a chilling murder. When the boy reappears in his life years later, the psychologist is drawn into a potentially destructive, soul-searching reinvestigation of the case. Barker delved into some of the issues I had been thinking about – philosophical questions about what evil is, whether it can be explained, let it alone treated. The novel explores the controversial issue of children who have committed murder, and how desperate people are for an explanation, any explanation, and how difficult it is to supply one.

When I read the book, I knew I wanted to adapt it to film. For me, the best way to deal with my grief and my anger was to channel these emotions into something else, something outside of myself, something I could examine and study.  And I also knew that my friend would approve. She had written a screenplay for a movie (Call Me,1988) about a woman who overhears a murder, which was eerily similar to what turned out to be her own death, recorded on the phone of the 911 operator.

In adapting the book to film, I was interested in probing the dark side of human nature. How does our dark-side express itself? As a culture, we are horrified and at the same time fascinated by evil. Maybe that is because there is an implicit awareness that there is a darkness in all of us – how close we all stand to evil. This scares us and motivates us to probe deeper, much like Tom, the psychologist and the protagonist, who embarks on a journey to explore this fundamental tension built into the fabric of human existence.

My friend’s son is due in court next month, for a hearing to determine if he has a “dangerous mental disorder” which will determine the length of his psychiatric commitment. He is now claiming the right to his mother’s life insurance policy and other benefits. So this story is not over. Is my friend’s son cured or is he a ‘walking time bomb.’ Maybe this is a question each person can only answer on their own.

At the end of my journey, which began with learning about my friend’s horrific death and continuing through the search for answers, by way of making this film, I don’t think I am any closer to understanding the moral complexity of what happened between mother and son. At the heart of the crime is an enigma, a kind of unknowability. We are so advanced as a society, it seems as though there should be an explanation, but what if there isn’t? This might seem like cheating, but perhaps withholding answers creates its own haunting resonance.

The film I made in response to this event is called The Drowning and opens at The IFC Cinema on May 10.