Most of us lead humdrum lives. We obey the rules. We open doors for strangers, we avoid cheating people, we get up and go to work and do what society expects. We may dream of breaking free and committing - for example - a massive bank robbery - to wreak revenge on a world we believe has unfairly ignored us - but usually the desire remains repressed, forbidden by conscience, social etiquette and, simply, the fear of being caught. 

Perhaps that's why we have a strange fascination for those whose lives have deviated drastically from the norm. And the greater the deviance, the greater our fascination. This week has seen the trial and conviction of Austrian Joseph Fritzl - who kept his daughter imprisoned in a dungeon for 24 years, raping her repeatedly and fathering children incestuously in the process. His actions were so depraved that they have triggered a whirlwind of publicity. Everyone has expressed outrage and horror over the case but few have attempted to ask "why?"

Scratch the surface of most non-profit driven criminality and the notion of 'control' is perhaps the most important word in our lexicon. We are powerless creatures and most of us - let's face it - lead pretty anonymous lives. Who'll be writing about us in 100 years' time? Will we be remembered at all? It's a cliche to say we'll be remembered by our loved ones. But once they too die, what is there left? We lack power. For some people this lack of power is shattering. It can lead to some people - those who lack a conscience or human empathy - taking extreme action to achieve a feeling of importance. Sometimes it's a single action - the case of Sirhan Sirhan, the man who shot Robert Kennedy in 1968, made just this point. "All America loves a winner and I was a loser," he explained when asked why he had assassinated senator Kennedy.

Sometimes, however, it's not just one random action. Some people create an inner sanctuary for themselves in which they gain that feeling of control they lack in the outside world. Gay serial killer Jeffrey Dahmer lured young men back to his apartment where he drugged and killed them before committing necrophilia. He then dismembered their bodies; detectives found human body parts everywhere in his flat. He killed so many people that the murders became almost routine. An unassuming and mild-mannered chocolate factory worked, Dahmer apparently lived for nothing else. By his own admission the thought of 'trolling' the streets in search of victims was the only thing that excited him. Sadism? Perhaps, but far more important to Dahmer was the attempt to establish a world where he felt in command and in control. A loser in the outside world, in the privacy of his apartment Dahmer felt he had established a special universe that lent him mysterious powers. He even built a kind of memorial to his victims. This special 'shrine' of grinning skulls, candles, dimmed lights and incense became a place of meaning to Dahmer.

Similar behaviour, if on a marginally less depraved level, can be seen with John Worboys, the former stripper turned London taxi driver whom some believe attacked up to 500 women in the back of his taxi. What is a taxi driver but someone who drives people from A to B? Relationships are seldom forged. You may make a decent living but few passengers bother to converse or make a friend out of you. It's a life of anonymity; one driver is the same as another. So Worboys sought to establish power in his taxi. He'd wave a plastic bag full of winnings at female passengers - in itself a bid to prove he was a 'somebody'  - and then offered to share a 'celebratory' spiked drink with them in the back seat before he assaulted them. He had turned his taxi into a prison for his victims in an attempt to turn a mundane job into something (for him) intoxicating and powerful.

This past week saw another perverted blast from the past. Charles Manson, now an old man of 73, was pictured in the papers, 40 years after his 'family' committed a series of incredibly brutal murders, most notably against Sharon Tate, actress girlfriend of Roman Polanski. Interestingly, Manson was pictured with a swastika on his forehead. It's perhaps no surprise that tyrants are drawn to Hitler. In the past Manson has said that Hitler "was a very tuned in guy" and expressed his admiration for him. Hitler was an extreme case of someone who sought to control the world. Believing that Jews were evil, he sought to destroy them in a fanatical mission. This extreme example of barbarity, racism and hatred still inspires people throughout the world, not only through its ideology but in terms of its extreme power in itself - an attempt to overturn conventional values of human equality, compassion and humanity.

That all the aforementioned people are evil is undeniable. But that shouldn't stop us scrutinising them. Simply dismissing them as "monsters" doesn't help us one iota. They may even be fit for the death penalty but we still need to analyse their behaviour - not in order to excuse or exonerate in any way, but simple for us to get a better understanding of aberrant human psychology and even to help spot other deviant behaviour in the future. British writer Brian Masters has done a lot of good work in this field and should be commended for it. It's all to the good that somebody does because delving into the darker realms of human psychology may help to prevent more cases like Fritzl's and Dahmer's in the future.