Why does terrorism fascinate me? Because of the terror in my past.

For example, when I was facedown on the floor in the middle of an armed robbery, a sense of calm enveloped me. I didn't panic when I returned once to my hotel room in Lahore to find Pakistani intelligence officials rifling through my luggage. I assumed that my unusual response to danger was unique to me. I had no idea that these reactions were well-studied aftereffects of trauma.

I consulted a therapist, not about my lack of feeling, but because I wanted to feel even less. It seemed to me that feelings got in the way of life. She told me that some of the qualities I assumed I had been born with -- including heightened sensitivity to sudden movements, scents, sounds and light -- were actually markers of trauma. She suggested that I might have post-traumatic stress disorder.

I did not believe it. I knew about PTSD from working with soldiers, and I could not imagine that my own life experience would result in similar symptoms. I had long ago brushed the memory of my rape aside; I thought I had "moved on." I wanted to contribute to society rather than remain stuck in the past, cringing in terror.

And yet, terror had become my central preoccupation. I felt compelled to understand the deeper motivations of those who hurt others. Instead of feeling terror, I studied it.

After I completed my second book on terrorism, I realized that I wanted to understand what had happened to me during and after my rape, a time I scarcely remembered. I had started another project, this time about the role of fear in how people respond to terrorist strikes. I needed an example of what it feels like to be scared to death. I thought of my own experience -- a forced march through the house under threat of death from a gun-wielding rapist.

In 2006, I requested a complete copy of the police report. Until then, I had never connected my work on terrorism with my own experience of terror.

Before I could see the file, the police had to redact the other names in it. As they read through it, they realized that a child rapist might still be at large. Pedophiles grow old like the rest of us, but they often continue committing the same crimes unless they are physically stopped.

The police required my help. But I also needed theirs. Just as I wanted to understand the motivations of the terrorists I interviewed, I found myself needing to understand my rapist, as a way to tame a terror that I was beginning to feel for the first time.

I felt compelled to answer questions I had spent my professional life asking about terrorists: What happened to the boy who grew up to become my rapist? Was there anything in his life story that might explain, at least in part, why he would want or need to hurt us? What happened to him afterward?

The police and I, working together, were able to find out a great deal about the man who attacked my sister and me. We discovered that between 1971 and 1973, he raped or attempted to rape 44 girls, 20 of them in one eight-block area near Harvard University. He was convicted of three of these rapes and was sent to prison for 18 years, only 10 days after he attacked us. Although the police knew of this man at the time and had information on a remarkably similar series of crimes that took place in the Boston area two years prior to our rape, they did not put the pieces together. For 33 years, most of these crimes remained unsolved. The rapist committed suicide several years before I began this investigation.

I had questions beyond the identity of my attacker as well: Why does the threat of violent death alter some of us, even if subtly, forever? Why does it make us unusually numb or calm when we ought to feel terrified?

It was only after I began research into my own rapist, whom the police and I discovered had probably been abused by a priest, that I thought more about the connection between the terrorized and the terrorists. I realized the possible importance of the frequency of rape of students at the radical madrassas I studied in Pakistan. I have felt, in my interviews of terrorists, that there was an element of sexual humiliation at work, but it was rarely more than an intuition on my part. Could sexual traumas contribute to contemporary terrorism?

Today, my work is moving in a new direction. A group of psychologists at Children's Hospital Boston has been studying the health issues of Somali American youth, with a focus on trauma. I am working with the group to study a question of recent national concern: why some Somali youth in this country run away from home to join al-Shabab, a Somali terrorist group that claims to be aligned with al-Qaeda. Is there a link between possible abuse and alienation and vulnerability to terrorist recruitment? Could terrorism sometimes reflect a kind of perverse post-traumatic evolution?

I have never had a problem talking to terrorists bearing Kalashnikovs. But I was petrified to talk to victims, afraid that their terror might elicit feelings I'd long avoided. After interrogating my own past, I am not avoiding them anymore.

info@jessicasternbooks.com

Jessica Stern serves on the Hoover Institution Task Force on National Security and Law. This essay is adapted from her latest book, "Denial: A Memoir of Terror," which will be published Tuesday. From the archives: Jessica Stern's most recent Outlook piece was "5 myths about who becomes a terrorist" (Jan. 10).