Not long ago, Roy became a type of monster. The transformation took a year and a half, and now, one morning each week, he sits in a room of similar cases. 

The windowless room is plain, with a blue industrial carpet, a circle of brown cushioned office chairs, a blackboard, a pair of unused conference tables pushed to the rear wall and a faint hum from the air ducts. To reach it from the waiting area -- on the second floor of a probation building in Connecticut -- Roy and the other men walk down a series of corridors and around a series of turns that feel like a path through a maze. The room is wedged in a back corner. 

''No one,'' a probation officer said, ''likes to think about what's back there.''

Roy wonders constantly how he wound up in this place, in the circle of 10 or 12 chairs, a circle of child molesters. 

His story begins on the beach and ends on the Internet. It seems to him that he was, only recently, a normal man, about 40, running a crew of technicians, repairing elaborate, computerized telecommunications equipment for Wall Street trading firms and in his off hours leading a wedding band, singing Frank Sinatra and Barry White at the Plaza. 

For a hobby, he flew kites -- kites bigger than most living rooms, brilliantly striped, with rippling streamers and ''space socks'' trailing more than a hundred feet behind, kites that could perform ballets when he held the lines. 

He recalls no history of longing for young girls. He had no criminal record of any kind. But then one summer, on vacation, his second wife pointed out her 11-year-old daughter's body. Roy and his wife were standing on the sand; his stepdaughter and her best friend played several yards in front of them at the edge of the surf. 

''Look at those girls,'' Roy remembers his wife saying.
''They're changing already. You can see their bodies changing.''

Roy has a soft, smooth face and an easy, engaging smile. (At his request, I've shielded his identity by using a nickname some of his former band members gave him.) Now in his mid-40's, he's round in the middle and broad in the shoulders; there's something bearish about him, but in a way that's more panda-like and cheerful than threatening. 

Nearby along the circle sits an elderly man with a graceful wave of white hair combed back from his forehead. There's a well-scrubbed blue-eyed man in his mid-30's, wearing a button-down shirt with a pleasant check of pale blue. 

Like the rest, they're here by court mandate for group counseling as part of their probation. Most, including Roy, have served time in jail or prison, from a few weeks to several years. The man with the wave of white hair touched the vagina of his grandniece; he kissed her chest and had her hold his penis. This happened repeatedly when the girl was between 7 and 9 years old. 

As an adult, the man in the checked shirt performed oral sex on his 11-year-old brother and later took his 6-year-old daughter to a motel room along with his brother, who was by then 16. Living out a fantasy he'd had for months, he persuaded them both to undress and urged his brother to have sex with his daughter, only desisting, only waking from the trance of his desire -- 

''seconds away from something really, really bad happening,'' 

he has told me -- when his brother began to cry.

''What possessed me?'' Roy asks in one form or another in the group sessions that I've been observing for close to a year, in conversation with me and, it is clear, alone with himself. It's a question that seems to churn through the thinking of most of the men. The one who longed to watch his brother and daughter, and who is a published poet, has talked to me about feeling like Dr. Jekyll and Mr. Hyde. In group one morning, another convict made reference to ''Dr.
Jekyll and Mr. Heinz.''

How does a man enter the realm of the monstrous? How broad or thin is the border between the normal and that realm? 

''Could anybody end up getting into this mess?'' 
Roy once asked me plaintively.

"Focus your awareness on your feet,'' Patrick Liddle, the group's therapist, its leader, instructs the men at the start of many sessions. They sit with their hands on their thighs, their eyes closed, as he teaches them a relaxation technique. 

''Now allow your awareness to move up to the center of your chest.'' 

He speaks in a soothing monotone, the voice he maintains with them always no matter how disquieted their crimes make him feel. Part of his job is to give them methods to keep their lives under control, to keep themselves from molesting again. This technique is one way. 

''Center your attention on the steady beating of your heart.'' 

He wears fashionably tailored suits and shoes polished to a low gloss. The clothes are part of the program. Liddle's boss sets the dress code for his staff, an attempt to confer value on those in treatment, men who could hardly have fallen lower. 

''Picture in your mind a large open field covered in deep grass up to your waist.'' 

Roy and the others sit perfectly still. Their fingers curl gently. Their jaws are slack; their mouths, slightly open. They seem almost to be sleeping, and like sleeping men anywhere, they look almost like children. 

''Now slowly open your eyes.''

They return from the field of tall grass to the faces of the other men. Liddle sometimes asks them for introductions, though the faces stay mostly the same.

They go around the circle. 

''I was convicted of two counts of sexual assault four and three counts of risk of injury to a minor and enticing a minor over the Internet,'' 

Roy began during a session months ago. He managed not to mumble. Facing up to what he has done, he knows, is a requirement for graduating from treatment. And this might lead, he hopes, to a judge's reducing his term of probation. 

The treatment theory is basic: to acknowledge both his crime and the anarchy of lust that lies within him is the first step toward his finding self-control. So the ability to confront himself -- and to be candid with Liddle about his sexual yearnings -- is a requirement, too, if he wants to do anything outside the bounds of his probation restrictions: visit his parents over the state line in New York or go to a bowling alley or a movie or a family function, anyplace where he might come in contact with children under 16. Any family gathering he attends must be adults only; he has to leave right away if kids show up. 

The group leaders and probation officers work in tandem, evaluating how well they can trust the men, and the therapists can be at least as wary as the probation officers. 

(In Connecticut, counseling is ordered for almost all sex offenders on probation, and the state-financed organization Liddle works for, the Center for the Treatment of Problem Sexual Behavior, handles nearly all of it.) 

Together, Liddle and Roy's probation officer set the limits on his life.

''I was sentenced,'' Roy continued with his introduction, ''to 20 years suspended after 30 days, with 35 years probation. My offense behaviors I engaged in were touching my wife's daughter and her best friend sexually, touching them through their clothing between their legs, around their waist, moving my hand into the top of their waistband. I also moved my hand under their shorts up to their panty lines. I used games that were called 'Chase' and 'Spider' to manipulate them into feeling safe with me.'' 

His voice quieted as he hurried on toward the end, toward the part of his story that holds echoes of recent, well-publicized cases -- like that of John Dexter, the headmaster for a quarter-century at the Trevor Day School in Manhattan, until his arrest in 2003 and guilty plea last year -- of apparently ordinary men going online to seek out sexual conversations and often to arrange to have sex with adolescents, with children.

With more detail than he gives in group, Roy has told his story as he and I have sat together at his home and at his job. 

He is still a supervisor at the telecommunications repair company. In a bland suburban building just off a highway, at worktables in vast, orderly rooms, he and his team lean over high-tech consoles with exposed intricate wiring and microprocessors with multicolored flashing diodes. They fix circuitry or, if he deems it necessary, redesign it. With the permission of Liddle and the probation department, Roy is allowed to work around computers as long as he never goes online outside the watch of a colleague. 

Everyone at his job is aware of his crime. He has made a point of answering everyone's questions. The company's owner, who has known Roy for five years, testified on his behalf at his sentencing. 

''You're talking about a person I know,'' the owner said to me. ''If you told me about a stranger I would write them off, I wouldn't talk to them, I wouldn't see them -- if they did one-tenth of what he did.'' 

At  Roy's job, the element of personal forgiveness goes beyond employment. As I drove with him to work after one of my first sessions with the group, he said that he was engaged to be married again -- to a bookkeeper at the company, a colleague since before his offense.

When Roy has spoken with me about his crime at the well-burnished kitchen table in his small, neatly kept wooden house or in an empty conference room across from the repair stations at work, he starts with the words of his stepdaughter's mother at the beach. 

No matter how common -- 

''Look at my daughter, how pretty she's going to be when she grows up; I'm going to have problems with her when she grows up'' -- 

they have a serpent-like quality as he tries to sort out what followed. They were ''the first trigger,'' he has said. Before, he doesn't think he saw his stepdaughter in any erotic way. He had known her and her older brother from the time they were born; he had been with their mother since they were around 4 and 6. (He has no kids of his own.) 

The children lived with their father, an executive, a man Roy grew up with. But they spent a fair amount of time at the home Roy shared with their mother, and after that vacation at the
shore, the games Roy played with his stepdaughter, and frequently with her best friend, grew sexualized -- at some level -- in his mind.

During ''Chase,'' they would turn off most of the lights. Often they plugged in a strobe light from his band equipment or a lamp that cast the shapes of moons on the walls, in blues and yellows and greens. 

His marriage, at that point, was falling apart. Sometimes his wife was home, having shut herself in their bedroom for the evening. Sometimes she was out on her own. He raced after the girls through the house, through the colored beams. In ''Spider,'' each player had to sit motionless; if you moved at all you got pinched. The touching occurred during the games. 

The confessional -- and dutiful -- introduction Roy delivers to the group implies that the touching was blatantly, consciously sexual on his part, but though he is obsessively introspective about all that took place, he can't seem to figure out whether this is true.

He remembered, with me, his anger at his wife, the fleeting thought that if she was going to leave him taking care of her kids, then he was ''going to get something out of this, too.'' Yet he recalled that there was no real sexual intent at that stage, not even any dalliance with fantasy, that often he didn't want to deal with the girls and their demands that he try to catch them; he didn't want to be bothered. 

''I don't think I ever touched them in their private areas,'' he said, making a distinction between those areas and the edges of underwear. ''Grabbing them, pulling them, knocking them down. Them jumping on me. It was still just teasing and playing with them. It wasn't like I wanted to have sex with them. Is there a difference?'' 

These kinds of questions reel through his memories. He can't settle on single answers.

''But was there sexuality behind it?'' he asked once while we talked. He replied
immediately, ''Yes.''

The erotic became explicit, Roy said, when they were in separate rooms, at separate computers. The layout of the house mirrored the one he owns now, many towns away. There was a series of rooms along a narrow hall. The basement was crowded with his guitars and keyboards and recording equipment. His stepdaughter was 12 -- though he doesn't face up to reality easily on this point. 

The first few times he came to this part of his story, he told me that she was by then 14, maybe 13. During his introductions in group, he doesn't mention how old she was; for a short while I didn't know her true age. When I read an old article from a local newspaper about the case and told him that it put her age at 12, he insisted that the article was mistaken. Only after I had asked him repeatedly did he call me one morning: he had just phoned his sister and ''found out'' that the newspaper was right.

When she was 12, then, one evening she sent him an instant message. She asked what he was doing. He was in his office; she was in her bedroom down the hall. He told her he was working on band contracts. She wrote that she was bored, that none of her friends were online. He responded that her brother had been giving their mother trouble, that she was completely different, that she was ''a really good little girl.'' According to Roy, 

''she came right back to me and said: 'Roy, you don't know me. I'm not a good girl,
I'm a bad girl.'''

She wouldn't tell him what she meant, but he had been smitten with what he had seen as the wild streak in her mother, back when she had left her husband for Roy, and now, right away, his imagination ran along sexual lines. 

''Oh, God, the apple doesn't fall far from the tree,'' he recalls thinking; he told me, regarding the effect of that instant-message exchange with his stepdaughter: 

''You couldn't have drawn me in any faster. I still remember it. Not excited as arousal excited, but excited as I gotta know more. Major adrenaline rush. I felt myself go flush. I was already overloaded. I finished the contracts I was doing, but I got off the computer right after that, and I went immediately downstairs and started playing.
That's what I always do when something's really got me; I need to shut it off. I had to shut that off at that moment. I had to calm it down. Put my headphones on. Had my guitar. I have this jazz routine I like doing. I do a jazz version of 'Blue Skies.' 'Polka Dots and Moonbeams' -- it's a slow jazz tune. I have about an hour's worth of music, and I just have to concentrate on the chord changes and the progressions, and it clears my mind. The only problem is,'' he raised his voice, almost shouting to me across the kitchen table, ''it didn't help.''

Soon he loaded his computer with a software program that would allow him, because of the way his and his stepdaughter's computers were interlinked, to monitor her online conversations. 

That day, alone in the house, he stepped back and forth along the hall, between rooms, between PC's, making sure his system worked, that she wouldn't be able to detect his lurking. And the next time she came over and logged on and started chatting with her best friend (the same girl he had chased through the house), their words ran across his screen.

His stepdaughter's romantic explorations, confided to her friend, became his pornography. Each time he monitored her conversations (about 7 to 10 times over several months, he thinks), he would have a soda and popcorn and 

''put my feet up on the desk, and I watched this thing unfold. 'Cause you have to understand, it's not something I would masturbate to while she was on the Internet. It would almost be like an aftermath of it. 'Cause it had your mind so cranked you had to have some relief. At any point I thought this girl was going to have sex with this boy. That's how intense this was.''

He didn't worry that she would walk down the hall and find him reading her words.

 ''Impossible, because my computer didn't face the door, and it would have taken
a split second to shut it off, literally,'' he said.

''Nobody could catch me, nobody. I'm too good. I'm too good with computers, trust me. I set up that PC so that when I shut the computer off everything was erased. So there was no trackable record on those PC's. It was wrong. So wrong. I put myself in such a bad situation, and I just fell into it. I guess that's how a drug addict gets. Once you've fallen into that, and you've gone in, it's almost like that's it: now you've got it in your head, and it's not going to go
away.''

The direct instant-message exchange between him and his stepdaughter continued every so often during the period of his monitoring. 

''She would sign on and say something to me, and that's when the conversation started. And I would flip it. She didn't start it sexually. I always flipped it. Just so you know. She didn't do it. She was a kid.''

He would ask her to ''show me something.'' She would refuse. He asked her to have sex with him. She told him no. He wrote to her, in one of their final Internet conversations, months before her 13th birthday, that he was going to step out of his office and into the kitchen to get a soda. He wrote that if she wanted to see what he wished to do with her, she should walk into his office and click on a window that would be on his screen. She left her computer and walked to his. When the window opened, a video showed 

''a man rubbing his penis on a girl's vagina that's been shaved,'' he said. 

A moment later, they passed in the hall. He remembers her calling him ''disgusting'' and each of them going quickly back to their own PC's. 

Petrified that she would report him, he begged her over the Internet to meet him on the stairs to the basement music room, promising that he would stay at the bottom. He pled his apology as she sat at the top of the stairs. Then she was gone.

Soon afterward, I learned recently from her father, she told her stepmother for the first time about Roy's ongoing solicitations. (Her father had just left on a business trip.) Her stepmother then sent her to Roy's house so that, assuming he would proposition her yet again, she could print out his words for evidence. She did. 

He was swiftly arrested. It had been about a year and a half since that trip to the beach. In court, he pled under the Alford Doctrine -- a legal acknowledgment that the evidence against him was sufficient to prove his guilt -- to the charges he lists each time he gives his introduction. He has been in treatment now for around 17 months. 

''I'm so embarrassed,'' he said to me at the kitchen table. ''I can't believe I did this. You know, I just don't know how I got myself there, I really don't. It makes me sick.''

Roy looks that way -- ill, aghast, mortified -- whenever he finishes his account. His full cheeks
appear almost gaunt, as though he has just emerged, barely, from the siege of some terrible infection. To see him like this is to feel that he would never allow himself to come anywhere close to repeating his crime. 

It is to understand what the owner of the telecommunications repair company -- where Roy's existence can seem so ordinary as he goes about his work -- once told me about his wife's opinion of Roy: their own children are grown, but she would have him in their house even with kids around. 

''That,'' the owner said, ''is the confidence that he gives you.''

Yet to think back over Roy's shadings of his stepdaughter's age and to hear his explanation that he wasn't lying to me but somehow no longer knew that she had been 12 is to feel less confident. Whether he has tried to deceive me or himself, this is exactly the kind of evasion, the kind of diminishment of hard truth, that would worry Liddle; it's a sign that Roy may not be capable of self-confrontation and self-control. And then I discovered, in a statement his stepdaughter made to the police, that some of the troubling touches, through clothes, began when she was in second grade. 

To have heard his consistent denials about this, his certainty that back then there had been only innocent games, is not only to wonder if she has imposed the taint of recent events on earlier moments but also to wonder if anything Roy says can be believed. And then when I learned, from the transcript of his sentencing hearing, that he used Freekypeephole as his Internet screen name, I could see him, simply, as a dangerous creep -- except that when I asked him about this, he recited the lyrics of a disco song he wrote and recorded back in the late 70's, a song called ''Freaky People,'' about the drug use he observed at Studio 54. (His father was an alcoholic, and Roy has never been much for drugs or alcohol.) 

He recounted that the song got some airtime on a major radio station, that because of this he wanted ''Freaky People'' as his screen name, that it was already taken, and that his server supplied the alternative, Freekypeephole, which he accepted well before his crime as a joke. 

My sense of Roy shifts back and forth ceaselessly, from perceptions of basic normality to those of extreme aberrance, from guarded trust to deep unease. But one constant is the reverberation of his words: 

''I just don't know how I got myself there.''

How did he get there? 

What are the causes of child sexual molestation, which is committed against perhaps 20 percent of girls and 5 to 10 percent of boys under the age of consent in the United States, according to David Finkelhor, the director of the Crimes Against Children Research Center at the University of New Hampshire. 

(Finkelhor, who has examined the studies extensively, added that the numbers range widely from 10 to 40 percent for girls and 2 to 15 percent for boys, depending on definitions and methods. The victims are preadolescents about as frequently as they are older. Most are abused by someone they know, often by a member of their family.) 

What parts are played by biology, by an abuser's own childhood, by aspects of isolation in his (for males make up around 90 percent of offenders) current life -- or by the powerful arrival of the Internet into the world of Eros?

Calling psychiatrists and psychologists, researchers and clinicians, who have been working in the field for decades and asking about origins and explanations, I have heard in response regret and laughter. The laughter came from Dr. Martin Kafka, senior clinical associate in psychiatry at the Harvard-affiliated McLean Hospital in Belmont, Mass., where he studies and treats sexual disorders. 

''I'll give you a quick answer,'' he said, cutting me off at the word ''causes.'' 
''We don't know.''

A much longer answer followed, his words propelled at high speed by his fascination with the subject: studies of sexually deviant brains have scarcely been done; there is 

''one suggesting hypothalamus abnormality, but really, the research is in infancy.''

The data show that sexual abusers of children are more likely than the general population to have been child sexual-abuse victims themselves but 

''most pedophiles have not,'' he emphasized, ''been sexually abused.''

(And here I thought of Roy talking about the men in group who were ''abused as kids something fierce, so I must be a real piece of crap, because I was never abused.'') 

Research indicates that ''social skills deficits'' can be a factor. Kafka's voice rushed on as he tried to construct for me some sense of coherence from what scattered scraps of knowledge exist.

''There is nothing coherent that's been established,'' Dr. Robert Prentky, a forensic psychologist at the graduate school of criminal justice at Northeastern University, told me.

''Frankly, in my opinion, there has been very, very little progress in the area of
etiology.'' 

And Dr. Fred Berlin, associate professor of psychiatry at the Johns Hopkins University School of Medicine, talked about society's discomfort with any scientific inquiry into sexuality, let alone into the causes of pedophilia. 

''There is inadequate funding, too little support for this kind of research,'' he said. ''We can't get beyond the moral to the scientific. These are considered vile people. There is an aversion to studying them.''

I asked about the Internet, whether it may bear any causal responsibility along the path toward offending.

''It's a fairly complicated issue,'' Berlin said, and one for which there appears to be, again, no solid research. ''I wouldn't go so far as to say that the Internet creates desire, but I do think it is creating significant difficulties.'' To some extent, he explained, it is merely a ''new and different vehicle'' for those who would offend against children anyway. But it ''provides temptation for some who might not otherwise have crossed the line.'' 

He added: 

''There are three areas of concern. 

Over the past decade, with the surge in Internet use, there has been no spike in the overall number of cases of sexual abuse against children. 

(There has been, it appears, a significant decrease, attributed by some to the success of harsher sentences and offender registries and by others, in part, to the possibility that those sentences and registries discourage victims, who tend to know their abusers, from reporting the crimes.) 

But Berlin's concern was echoed by Prentky when he described the Internet as

''a catalyst for fantasy and dangerous if the control over behavior is markedly impaired.'' 

And by David D'Amora, Patrick Liddle's boss and the head of the Center for the Treatment of Problem Sexual Behavior, who has about 800 child sexual abusers under his watch in Connecticut, when he talked about the Net's abundant porn and disembodied chat-room conversation as a ''disinhibitor.'' 

And by Liddle himself, whose normally tempered voice nearly rose to a yell when I asked whether online porn might provide a safe outlet for otherwise destructive erotic drives: a man masturbates; the craving subsides. ''No!'' he replied. He was thinking of the men in that back room at the probation building. 

''That's like an alcoholic saying I'll only have a couple of drinks, I'll only have low-alcohol beer.'' 

And then he was thinking of everyone when he said that pornography

''desensitizes people so extraordinarily.''

When Roy tells his story, he insists that he never visited any Web sites of child porn. He doesn't think there is much relevance in the mainstream porn that he did view -- and it doesn't seem to have had, for him, the erotic impact of his stepdaughter's conversations with her best friend. But he claims (perhaps too self-servingly) that he would never have propositioned his stepdaughter had it not been for the Internet's unique, oddly dehumanized form of communication. In the ultimate moments, he beckoned her to his computer. He beckoned her, physically, into his space. But before then, his lust gained much of its unbearable power, and found its most intense expression, screen to screen.

One day this fall, Roy sat behind a gray laptop that rested on a metal desk. Martina Kardol, one of Liddle's colleagues, stood over him in a small office in the probation building, reading aloud from a set of instructions. He would be shown 160 images on the laptop screen, she informed him. Her voice stayed level; her face, expressionless. She has long blond hair and wore a loose sweater with black stretch pants. (Not all the therapists adhere to D'Amora's dress code.) ''You will see people of varying ages.'' Roy had on a black blazer, a tie and sharply pressed khakis. From here he was headed straight to an important meeting at work. ''Imagine being sexual with the models in the slides.''

Kardol told him to score each picture for sexual interest, hitting 1 for ''disgusting'' up through 7 for ''highly sexually arousing.'' He should advance through the images by clicking the return key. He was shown a practice set. A blond woman in somewhat prim white lingerie; then a clean-cut man in a plaid shirt and khakis; then a boy, who looked to me around 12, straddling a bicycle with a book bag over his shoulder; then a girl around the same age wearing a straw hat and eating strawberries; then a pudgy little girl of maybe 4 in a blue one-piece swimsuit. Kardol asked Roy if he was ready. Sitting upright, ever compliant, he said that he was. We left him alone with the photographs.

He was taking the Abel Assessment for Sexual Interest, as all the men do at some point during their treatment. It offers a gauge of erotic preference measured not by the 1 to 7 ratings but by the length of time a man lets his eyes linger on each image. The photos are fairly demure. Legally, the test can't show pornographic images of minors, so to keep things balanced, even the adult pictures are less than revealing. And when, later, I clicked through a sampling, the distinction between age categories sometimes eluded me. The subjects in the pictures are supposed to represent four plainly separate age groups so that areas of attraction can be clearly measured.

There are children of 2 to 4, children between 8 and 10, adolescents between 14 and 17 and adults at least 22. But some of the 8-to-10's looked to me almost like young adolescents. And some of the adolescents appeared more like young fresh-faced adults, with the kinds of faces and bodies you might see on billboards selling underwear, before I reminded myself about the likely ages of the models in some of those ads. Still, the Abel Assessment is widely considered a strong diagnostic tool, and when Roy came to Kardol's office door a half-hour later to say that he was finished, he looked faintly shellshocked, like a patient who had been through an arduous diagnostic exam. The information was sent down to the Abel offices in Atlanta, Ga., and Kardol soon got the results. Roy's attractions were for adult females and -- very slightly more so -- for females in the adolescent category.

This put him, Liddle explained to me, within the realm of ordinary male sexuality. The minimal preference for adolescents over adults was, he said, a cause for some worry, given Roy's crime. But in itself the strong erotic response to adolescents was entirely normal.

Along the circle, during my time with Roy's group, there have been a few whose Abel results were plainly aberrant: men drawn above all to preadolescent boys and men drawn powerfully and almost equally to disparate categories, adults and young children, boys and girls. Until his term of probation ended, there was a retired accountant who met the psychiatric definition of a ''fixated,'' or exclusive, pedophile. He had coached sports and built a clubhouse on his property in order to lure the neighborhood boys; he had spanked and groped many over a period of many years.

Yet most of the group tends to fall somewhere closer to the middle of a continuum -- a continuum on which normal occupies a broad and blurry sector. With most of the men he has worked with over the past 14 years, Liddle says, 

''the difference between me and my guys is a very thin line.'' 

He doesn't mean that he's on the edge of doing what they have done, only that the potential may lie within all of us.

''We want there to be the clear line; we want there to be the sloped forehead,'' 

David D'Amora has said, summarizing society's thinking about the men in groups like Liddle's, men D'Amora has been watching over for the state since 1986. Before that, he was a therapist for adult and child victims of sexual assault. 

''It just doesn't exist. We want them to be the few, the perverted, the far away. Most are not.''

What research has been done seems to back this up. 

Dr. Richard Green, a psychiatrist at the Imperial College School of Medicine in London and professor emeritus of psychiatry at U.C.L.A., wrote two years ago in the journal Archives of Sexual Behavior about a 1989 study: the psychologists John Briere and Marsha Runtz found that 

''in a sample of nearly 200 university males, 21 percent reported some sexual attraction to small children.'' 
Specifically, 
''9 percent described sexual fantasies involving children, 5 percent admitted to having masturbated to sexual fantasies of children and 7 percent indicated they might have sex with a child if not caught. Briere and Runtz remarked that 'given the probable social undesirability of such admissions, we may hypothesize that the actual rates were even higher.''' 

Green wrote as well of the work done in 1970 by the researchers Kurt Freund and R. Costell. Forty-eight Czech soldiers were hooked to a ''penile responsivity'' meter known as a plethysmograph. Viewing a series of slides, 

''28 of 48 showed penile response to the female children age 4-10.'' 

And to count Web sites or consider legal history is to sense that the results of these studies may represent an unspeakable reality. Type in ''preteen porn'' on AOL's search engine and the list of sites covers thousands of pages. Until the late 19th century in England, the legal age of sexual consent was 10. 

''They are not monsters,'' Joan Tabachnick told me. ''They are us.'' 

Tabachnick is the director of public education for Stop It Now!, which was founded by a sexual-abuse survivor and which is among the most prominent national organizations devoted to the prevention of child sexual abuse. 

''It's so much easier,'' she said about the prevailing public vision, ''to think only of the most sadistic, most dangerous pedophile,'' the predator who kidnaps and abuses and kills. ''It's very comfortable. We can say, They're not who we are.'' 

But they're also not, she pointed out, the typical offender. They are the rare extreme. 

''It's very uncomfortable,'' she went on, ''to say, I know what it means to look at my child as a sexual being -- I know what it means to want to touch my child.'' 

She was not excusing molestation; she was calling for a complex understanding of a widespread and often devastating crime, because without it, she said, efforts at prevention are crippled. She drew a comparison with adults' acknowledging their wish to hit their children in moments of rage -- mere acknowledgment can make the impulse easier to quell, and those drawn hard to such violence can seek help.

''It's far more difficult to be candid about sexual urges,'' 

she said, and so it's far more difficult for those on the edge of offending -- those for whom cultural taboos, legal prohibitions and empathy for the child aren't powerful enough to keep desire deeply submerged or to choke it off if it rises to the surface -- to find a way to stop themselves.

After the relaxation exercise and after the introductions on days when they are given, the men lift their loose-leaf binders from the floor beside their chairs. The books are filled with the homework they've done and the handouts they've been given, with ''feelings journals'' and instructional sheets on methods like ''Thought Broadcasting'': 

''If you get a deviant thought, imagine that your thought is being broadcast from your mind over a loudspeaker system.''

Roy's binder is the thickest of all. He tries to think of treatment like ''a normal college class,'' as if to convince himself that diligence will guarantee graduation. Not only does he have a jumbo white plastic binder with labeled dividers that he brings to group; he has another that he keeps at home. He throws away nothing. His homework and ''action plans'' -- his applications to do what his basic restrictions don't allow -- are composed at length and always neatly typed out. But lately, for Roy, things have not been going well.

The counseling takes what is known as a cognitive-behavioral approach. Back in the early to mid-1970's, D'Amora has recounted to me, when the field of child-molester treatment was just developing, the typical strategy was more psychoanalytic and individualized -- profound insight into the disinterred past was supposed to change behavior and reduce recidivism. It didn't, and by the early 80's, therapy shifted toward behavior modification, with offenders instructed to inhale noxious odors during deviant fantasies. 

Here there were signs of ''fair success,'' D'Amora said, followed by signs that the effect was often short-lived. The method has mostly faded from the field. Meanwhile, the cognitive-behavioral model began to be used more and more -- Liddle's sessions can seem as much like classes in coping skills as anything that might be called treatment. With a creased, stoic face and a manner that is habitually restrained, he keeps the fluorescently lighted room sedate. He asks the men to open their binders to a handout on ''dynamic risk factors,'' and they go over a list, from ''victim access'' to ''intimacy deficits,'' of things they need to avoid or try to overcome. Or he asks what deviant thoughts they've had over the previous week. 

To Liddle's question, I have never heard the men speak more than a very few words about children. Roy has told me that he's fantasized about his stepdaughter a good deal since his arrest, but he has never brought it up in group. (By court order, he hasn't seen her since then.)

One man has said to me, 

''If we talked in there about what was really going through our minds, we'd all be wearing ankle bracelets.'' 

Liddle takes what modest fantasies the men are willing to mention -- one morning, it's about a young-looking gas-station attendant someone has glimpsed -- and he reviews ''Thought Broadcasting.''

Liddle never presses hard toward the darkest truths. His approach is full of paradox. He explained to me that he aims to elicit candor -- but candor that is delicately calibrated. Detailed and wrenching confessions of illegal acts or illicit desire could destroy the composure and dignity he wants to instill in the men, partly through the air of unbreachable calm in the room. 

(Too much communal honesty could also stoke their fantasies. For this reason, the men are forbidden to talk with one another outside the meetings.) 

Liddle hopes to ''build up their sense of decency.'' He wants them to leave the program, which they usually do after about three years, believing in their own capacity for restraint.

This kind of treatment may work. 

The recidivism rate for child molesters is around 17 percent, according to Dr. Karl Hanson, a psychologist with the Office of Public Safety and Emergency Preparedness in Canada and a leading researcher in the field. Already far lower than the public tends to think, the rate may drop by as much as seven points with the completion of a cognitive-behavioral program like D'Amora's. Yet Liddle knows enough to feel uneasy, almost always, as the men move on.

He is uneasy about Roy -- and Roy is nowhere close to moving on. For a time, all looked positive. Roy's diligence seemed to signify honesty and control. The privileges he applied for were steadily granted. He could drive over the state line to visit his parents; he could fly his kites on his town beach. He was told that he might eventually be allowed to play music at a local bar. But not long ago Roy and his new bride, the bookkeeper from work, put in a request with Liddle that she be allowed to take a special training course the next time it is offered and that she then be appointed an ancillary, probation-approved supervisor so that the couple could have more freedom. 

Yet it turned out that Roy and his wife haven't told her parents about his crime. And Roy didn't make this clear to Liddle. Hiding his past from his in-laws may be entirely understandable: should he be expected to tell them? Have any of us constructed our lives without concealing portions of ourselves? But his not coming clean about this to Liddle is considered unacceptable. If Roy's wife wants to be in a supervisory role, her first concern has to be with keeping him away from trouble, like family situations that might involve contact with girls; to do that she needs to tell her parents the truth. When his in-laws' ignorance emerged, indirectly, during a later discussion in group, Liddle started to worry about the way Roy had deceived him.

Then Roy took a polygraph test, as the men generally do twice a year. One of the most powerful parts comes not when the machine is running but, beforehand, when the nervous offender fills out a wide-ranging questionnaire. Here Roy admitted, for the first time to anyone in the program, that he fantasized about his stepdaughter. Earlier, telling me about these erotic thoughts, which he seemed desperate to exorcise, he said that his treatment prevented him from putting them in the past. The thoughts were ''burned'' into his mind because he had to sit every week in that circle, and he could not bring himself to confess them in the carefully subdued atmosphere of the back room. Liddle, he said, 

''asks for deviant fantasy but he doesn't really want it.''

Liddle didn't see it that way. He saw a man in denial, a man trying to deflect responsibility for the force of his lust, a man who should have delivered, in group, a simple acknowledgment of his desires, just as he should have been clear about his in-laws. Other deceptions glimmered. In the evasion of truth Liddle saw the threat of chaos. He saw a man unable to confront himself or ask for help, a man who might unravel and repeat the past, if for example, his marriage were to deteriorate, if he were to have access to girls.

In mid-January, he moved Roy to a newly created group for higher-risk offenders. He had already taken away all Roy's privileges -- the kite flying, the visits to his parents. Roy has to start from scratch. Except for work, he is more or less housebound.

At his house, one recent evening, I met the woman who has married him. She is a few years older than Roy, but young-looking and trim, with brown bangs and a kind of Caroline Kennedy smile. This is her first marriage; she has no children. She and Roy sat side by side on a new couch with matching end tables. Outside, there were cute wooden shutters on the windows. She wore white socks on her shoeless feet. They had just finished their ritual Friday-night meal of pizza and eggplant sandwiches. In certain ways, the domestic scene couldn't have been more unremarkable.

They started dating a few months after his arrest but before his plea; probation's rules hadn't yet defined what he could and could not do. They went to the movies and bowled and flew his gigantic kites. He confided in her about his crime. 

''In my heart I didn't think he was this monster that he was portrayed as in the paper,'' she told me, referring to the articles in the small newspaper of his suburban town at the time of his arrest. ''I didn't know what to believe.''

On the couch, they reminisced about the purple-and-aqua stunt kite that she flew and couldn't manage on their first date. They laughed about the way it tugged her down the beach. He remembered her once saying to him, '

'When we go out flying, it's like an entire new day.'' She recalled, ''One of the nicest things he ever said to me was that when he met me, God was giving him a second chance.'' 

Her voice was sweet yet scarcely gave way to emotion. She could seem keenly realistic, as if she had thought everything through. But Roy had spoken in group about the meeting the two of them had with her family priest, who was about to marry them. They told the priest about his crime. When the priest asked her whether she was really prepared for a life with a convicted child molester serving 35 years probation, suddenly ''she cried hysterically.''

''I think,'' she said on the couch, ''I know Roy well enough'' to be sure that he won't ever do again what he did. ''I think with Roy things just got out of hand.'' 

She talked of hoping still to take the course for family members who wish to act as supervisors, so she could learn how to be on guard, how to save him. 

''People can stumble,'' she said. ''I want to be able to recognize the signs, to know what to look for.''

Then, for a few seconds, her voice sharpened severely.

''To this day'' -- she spoke partly to me but partly to her husband -- ''I can't understand how he could write crap like that to a little girl.'' She said she told him this frequently. ''She does,'' he mumbled, looking stricken.

One night, shortly before his privileges were taken away, Roy and his wife launched a vast, luminous gold-and-red kite at the town beach. Usually after dusk the beach was empty. But a group of kids came running toward them, boys and girls who looked, in his eyes, to be between 4 and 12. By his agreement with Liddle and the probation department, he was simply supposed to tell the kids to keep their distance, to tell them they might get tangled in the heavy lines. The mere presence of minors didn't mean he had to leave the waterfront. But he panicked, and whether fleeing some imagined legal transgression or terrified by something within himself, he left the unwieldy lines to his wife. He raced away.

He rushed for the waist-high fence that divides the sand from the parking lot. He couldn't get his bearlike body over it cleanly; he wound up stuck, sitting on it and crushing it. Sometime later he showed me the place of his flight, where the fence remained bent. It wasn't hard for me to picture him caught there, between the safe and the terrifying.