Missing from most accounts of cold-blooded killers, for example, is reasoned speculation about what they might have in common, beyond the horrific nature of their crimes and the usual suggestion that they were the unfortunate products of early psychological trauma or adverse experiences, such as poverty, emotional or physical deprivation or abuse, parental rejection, inconsistent disciplinary techniques, and so forth.

With respect to Clifford Boggess, the FRONTLINE documentary's frequent references to his harsh early childhood will no doubt satisfy many viewers that the explanation for his crimes has been uncovered. Others, myself included, would argue that such an "explanation" is post-hoc, scientifically unsound, and potentially misleading.

There is little doubt that the neglect and abuse of a child can cause serious psychological and behavioral problems, including depression, low self-esteem, suicide, acting out, and violence. But for every product of an abusive, dysfunctional background who commits a terrible violent crime there are scores of others from similar backgrounds who lead normal, productive lives. Further, many notorious killers were raised in warm, nurturing family environments. Most after-the-fact explanations of behavior, though well-intentioned and often interesting and seductive, usually are not very informative. Indeed, it is possible, with diligent searching, to find a "reasonable" explanation for just about any behavioral or psychological problem.

We don't know why Clifford Boggess ended up as he did. But, do we know what sort of person he was? Although the picture is far from complete, there are some clues.

Perhaps the most telling of the clues are the impressions of the FRONTLINE correspondent, Alan Austin, and the demeanor and words of Boggess himself. After some three years of intermittent interactions with Boggess, the reporter Alan Austin came away with the uneasy feeling that he was dealing with someone who was not quite human. Shortly before his execution, Boggess talked about his crimes and the possibility that he would meet in heaven the two old men he had murdered. He told Austin that one night he had addressed his victims by name: "I'm sorry, I wish I could take it all back. I shouldn't have done all those things--something reached down inside my gut. I mean it physically hurt down in my gut. And I sobbed, not just a tear or two, but a cry from the gut like I haven't had in years."

Commenting on this expression of remorse, Austin said, "This isn't the first time he's talked about tears. But, like other signs of sorrow or remorse, I've never seen one. The constant grin reminds me of what his uncle Carl said: 'He's a great pretender.'" Later, Austin commented, "He's done and said all the things he could think of to make himself human. It just hadn't worked."

Another example. Earlier, Boggess had read from a letter he had sent to the granddaughter of one of his victims, a letter that described in detail both murders, his remorse, and his salvation--through finding Christ. But, said Austin, "The confessions and the apologies, like those I've heard before, seem strangely off-key and mechanical, as though he were trying to become human, but doesn't know how."

These impressions certainly were consistent with the dispassionate, matter-of-fact manner with which Boggess described his crimes, as well as with his apparently cheerful, upbeat demeanor while awaiting execution. His statements about the brutal, senseless murder of two elderly men had about the same emotional tone as if he was recounting his performance in a baseball game or, more chillingly, about having hit a home run. Here was a man who seemed emotionally unconnected to the rest of humanity.

I was particularly intrigued by his demeanor during the days preceding his execution. Rather than being depressed, apprehensive, or concerned about his plight, he gave the impression that he was starring in a stage play, and that his execution would be the grand finale. Exit stage right to thunderous applause.

As Alan Austin suggested, Clifford Boggess seemed to know, at some level, that he was different from the rest of humanity. Like a blind man trying to understand what others meant when they talked about color, Boggess must have been puzzled by conversations about deeply felt emotions. I suspect that his attempts to simulate emotions affected people in different ways, in some cases appearing genuine (for example, to Conny Krispin, his pen pal from Germany), but in others seeming to be superficial, a bit off, mere mimicry, or poor play-acting. His difficulty in comprehending the emotional reactions of others was reflected in his letter to the granddaughter of one of his victims, in the casual accounts of his crimes, and in the ease with which he "kissed off" and replaced those whom he found no longer useful to him.

His last words were interesting, and perhaps attest to the larger-than-life role he had assigned himself. "I would like to offer up my death (sic) for the conversion of sinners on death row. Lord Jesus, into your hands I commend my spirit."

What are we to make of all of this? Perhaps not a lot, given that what we have to work with are selected slices of a man's life. However, the FRONTLINE documentary suggests that Boggess exhibited many of the characteristics that define psychopathy, a clinical construct consisting of a constellation of interpersonal, affective, and lifestyle characteristics.

On the interpersonal level, psychopaths are grandiose, arrogant, callous, dominant, superficial, and manipulative. Affectively, they are short-tempered, unable to form strong emotional bonds with others, and lacking in guilt, remorse, and empathy. These interpersonal and affective features are associated with a socially deviant lifestyle that includes irresponsible and impulsive behavior, and a tendency to ignore or violate social conventions and mores.

Although not all psychopaths are murderers or come into formal contact with the criminal justice system, their defining features clearly place them at high risk for aggression and violence, with predatory and instrumental overtones. For example, an FBI study found that almost half of those who killed law enforcement officers were psychopaths.

Particularly dangerous are psychopaths who are sexually "turned on" by violence. In this regard, it is noteworthy that the murders committed by Boggess were calculated, almost casual, attempts to prevent being caught for relatively small-time robberies. During his trial a woman testified that he became sexually aroused when talking about the first murder. About this incident he said, "Talking about the murder was not what sexually aroused me. At the time that she and I discussed it we were lying in bed naked. We were living together. We were lovers and we were in bed in the nude. And we discussed it. It was really more a thing of - I've told you what you want to know. Now that subject's over with. Let's start something new. And it was more my starting a sexual encounter to get her off of that subject and to get onto something different. There's nothing about the murders that sexually arouses me at all. There was nothing sexual about them. That's a misinterpretation."

He may have been right, although his explanation reminds me of an offender who said that he had an erection every time he robbed a bank because he was thinking about his girlfriend!

In one interview Boggess stated that had he not been caught he would have continued to kill. "After the second murder," he said, "I could already notice that with each successive time it would get easier not to feel. It would get easier to turn my emotions off to do what I was doing, and perhaps I would get better at it. So I would have kept on killing had I not got caught."

Given his stated motives for the first killing--self preservation, not getting caught, hurting the victim for the sake of hurting him--it seems likely that Boggess was already adept at turning his emotions off: "I was totally consumed by the task at hand and it kind of turned my emotions off for the time being. I wasn't allowing myself to feel any emotions." Of course, it would have been easy for him to do this if his emotions were already blunted or rudimentary.

Was Boggess a psychopath? Possibly. Although I can't be sure without much more information and without a formal assessment with a standardized instrument, such as the Psychopathy Checklist-Revised (www.mhs.com) But if he was, his behavior and the apparently inexplicable murders he committed become more understandable.

Like all predators, psychopaths have little empathy or concern for the feelings or rights of their victims, whom they see as nothing more than objects or possessions to be used in whatever way they see fit. They do whatever it takes--charm, manipulation, intimidation, violence--to get what they want.

Although the causes of psychopathy are unclear, it is likely that a combination of biological/genetic and social factors is at play. Early abuse, deprivation, and other adverse experiences are not sufficient to account for the condition.

Recent neurobiological research suggests that psychopathy is associated with anomalies in brain function, particularly in those areas of the brain responsible for the integration of emotion and cognition. These findings are consistent with clinical assertions that the cognitions, language, and life experiences of psychopaths lack intellectual and emotional depth.

Why do these cognitive and affective anomalies typically go undetected? For one thing, psychopaths effectively use their own personal attributes to put on a good show. Intense eye contact, distracting body language, charm, and a knowledge of the listener's vulnerabilies are all part of their armamentarium for dominating, controlling, and manipulating others. We pay less attention to what they say than to how they say it--style over substance.

This research is relevant to society and to the criminal justice system because very little of what we do is based solely on logical appraisals of situations and their potential ramifications for us and others. In most cases, our cognitions, interactions with others, and "conscience" are colored by powerful, deep-seated emotions. However, for psychopaths, emotions play only a minor role in motivating and guiding their behavior. In a sense, the conscience of psychopaths is only half-formed.

In most jurisdictions, psychopathy is an aggravating rather than a mitigating factor in determining criminal responsibility. Psychopaths are considered sane, both psychiatrically and legally. However, some clinicians and lawyers have suggested that the impoverished emotional life and rudimentary conscience of psychopaths put them at a disadvantage when it comes to adhering to the rules of society. For this reason, they argue, psychopathy could be viewed as a mitigating factor in a criminal case. As one psychiatrist put it, perhaps psychopathy will become "the kiss of life rather than the kiss of death" in first-degree murder cases. This would be unfortunate, because psychopaths are calculating predators whose behavior must be judged by the rules of the society in which they live. They have an intellectual awareness of these rules but do not follow them unless it is in their own best interest to do so. As the Innuit of northern Canada put it, "Their mind knows what to do, but they do not do it."

If psychopathy is ever used successfully as a defense for a criminal act, the flip side of the coin is that the disorder currently is extremely resistant to treatment, and any civil commitment likely would be permanent.

Those interested in learning more about recent theory and research on psychopathy can log on to my webpage where they will find an extensive list of publications on psychopathy, and a variety of articles and links to other web sites.

Robert D. Hare is the author of Without Conscience: The Disturbing World of the Psychopaths Among Us, Guilford Publications (http://www.guilford.com/)