As the disturbing crimes of Col. David Russell Williams come to light, many are puzzling over the many apparent paradoxes of this successful, married military man.

Williams rose up the ranks of his career while charming the dignitaries whose shoulders he rubbed. Yet, he also acted out fantasies of rape and murder, killing two women, committing sex assaults on two others and a string of fetish break-ins.

And that is what is so puzzling to most observers of this case.

Dr. Julian Gojer, a forensic psychiatrist with Toronto Western Hospital who also provides group and individual therapy for those charged with sex offences, says it's not unusual for sexual deviants to also be outwardly charming and normal-appearing, if only to disguise what's going on in their heads.

"Most of them are going to be successful members of society because they've learned to keep their sexual deviation under wraps," he tells

Gojer says most people suffering from sexual deviancies -- which doctors call paraphilias -- can become very adept at hiding their thoughts and living normal lives.

"It's when you have additional mental illnesses, when you have socialization problems, that's when you stand out as being odd or eccentric. Then it's more likely you're going to get caught," he says.

But there's another aspect of Williams that makes him appear to be a rare breed among sexual predators. While other serial killers, such as Ted Bundy or Clifford Olson, first ran afoul of the law as youths, Williams maintained a clean criminal record for his whole life, until now. The police investigation suggests Williams didn't even begin his break-ins until 2007, when he would have been 44.

Gojer says sex offenders often commit what he calls "low-grade" sex offences, such as peeping, for years without being arrested.

"One of the most common sex offences that you get are exhibitionist behaviours and some of my clients expose up to 10,000 times in their lifetime without getting caught," he says.

"It's quite easy to get away with low-grade sex offences. It's what happens when the person becomes confident, more brazen, and the person actually believes that they can get away with it," he added. "The more you get away with it, the more likely you are to repeat such behaviours or escalate such behaviours."

Dr. Brad Booth, a forensic psychiatrist who works at the Sexual Behaviours Clinic of the Royal Ottawa Mental Health Centre, says many sexual offenders contemplate their crimes for years before finally acting.

"Many individuals, prior to actually committing an offence, have fantasies about the offence, where they basically rehearse the events over and over before escalating to actually doing it," Booth told CTV's Canada AM.

Booth suspects Williams suffered from sexual sadism, which is a paraphilia marked by a sexual arousal at the humiliation of others.

"Often that alone isn't enough though for an individual to go on and commit these sorts of offences," he added, "Usually, you need some sort of disinhibiting factor."

Booth wondered whether Williams might have suffered from psychopathy, which is marked by charming behaviour and a complete disregard for the feelings of his victims. Gojer isn't so sure.

"I would disagree with that, because there are many sex offenders who are not psychopaths," he says.

"What I would say would be a more likely factor to make someone offend is the presence of stress, depression, some life event, because the person has learned to cope with stress by gravitating to their sexual deviation," Gojer says.

"The presence of psychopathy makes it more likely the person would be less focused on the victim's feelings, but it doesn't mean that the absence of psychopathy means the person isn't going to act," he added.

Gojer says the biggest question is what makes a sexual deviant start to commit serious offences. He says some exhibitionists, for example, remain exhibitionists for years and never move into other offences.

But he says it's common for people who have one sexual deviancy to also have another one.

"When you start having two or three deviations, one might feed into another," Gojer says. "Or when one deviation is no longer giving the person satisfaction, the person might then start gravitating to more serious forms."

But he stresses that is rare. He says he has treated a large number of people convicted of child pornography, but only a small portion of them have actually offended against children.

Gojer says the bottom line is that there are no hard rules when it comes to sexual deviancies.

"There is no one type of person, there is no specific personality that's typical of a sexually deviant person," he says. "You can find them in all walks of life and in all types of people in all types of professions."