Despite the best advice of the world's top experts, Australian documentary-maker Ian Walker was naive to think he could study a psychopath in the wild and not get hurt.

"I didn't really understand how manipulative a psychopath can be," the director of I, Psychopath now admits. "I thought it would be a fair fight. After all, the filmmaker has the power, really. The power of the camera and the edit."

But, as it turns out, Walker chose his subject well. 47 year-old Israeli-born Sam Vaknin is a former corporate criminal and a self-proclaimed master of manipulation and reinvention. Walker first interviewed him several years ago as the author of the book Malignant Self-Love: Narcissism Revisited.

Walker was intrigued by a throwaway line where Vaknin professed he thought himself a "corporate psychopath". Afterwards, the film-maker spent several years researching the subject, but always wanted to make a film which might show psychopathic behaviour in action. Because of his narcissism, Vaknin was almost certain to say "Yes".

So, in February 2008, joined by Vaknin's long-suffering but ever-loyal wife Lidija, the threesome embarked on a diagnostic road trip to the world's top experts in psychopathy. Via a battery of psychological testing and brain scanning experiments, Vaknin becomes the world's first civilian to willingly seek a diagnosis for psychopathy.

The scientists are pleased to meet him. The "non-violent" or "white collar psychopath" is a test subject they rarely find in their labs. Much about them, including how their brains work, remains a mystery.

"They don't come to the attention of the science but also not to the attention of the social system because they are not criminal," explains German-based neurobiologist Professor Niels Birbaumer. "They are not violent, viciously violent and that's why we don't know them. But their impact on society is tremendous, and it was never studied."

In I, Psychopath, there are effectively two films happening in parallel. As the encounters between Sam and the scientists unfold, the relationship between subject and director shifts and changes, inadvertently supplying a voyeuristic first hand account of what it is like to deal with an everyday "non-violent" psychopath.

Vaknin proves to be the real thing, scoring an 18 out of 24 on the official Psychopathy Checklist (Screening Version). Most people, outside of prison, would score a zero or one, according to the Checklist's inventor Professor Bob Hare.

Unlike most psychopaths, though, Vaknin is ruthlessly honest about his lack of feeling and his opportunistic predatory nature. His carefully controlled aggression worked, as Walker recalls, "like a slow poison on my mental health."

If the vocabulary of melodrama sounds a little extreme, Walker believes many people experience a sense of derangement, a kind of mental dysmorphia, when caught in the powerful grip of a psychopath.

"Given that experts now believe that one out of every hundred people qualify as a psychopath, there's probably at least one in every dysfunctional office. I've encountered minor versions working in the media," he laughs. "And most of them are way too careful to let the mask drop and get caught out. That's the problem. They are manipulative, talentless charmers who knife you in the back as soon as it gets dark."

The bullying, which Walker says is a stock-in-trade tool of the psychopath, started for him on Day One of the shoot.

"After the first interview in Macedonia, where Sam lives and had been working for the government as an economic adviser, he called me to a special meeting and read me the riot act. He knew we'd committed to the documentary, so he threatened to pull out. He accused me of asking negative questions, told me I was a terrible filmmaker.

"That was just the beginning. After that, the abuse came on an irregular and seemingly irrational basis, every other day. It was like death by a thousand cuts. But he was very callous and controlled. He never did or said anything in front of the camera, he always waited until the main camera was turned off, or safely packed away."

Like most psychopaths, Vaknin knows what he's doing and is a skilled manipulator. It's his full-time pursuit. In one of the most insightful and informative scenes in the film, Vaknin launches into a vicious and foul-mouthed verbal tirade against Walker then, moments later, coolly dissects the art of bullying.

"Many systems in the body go haywire within a session of bullying," he tells the camera. "Especially once the session is over. So what bullies usually do is they start and stop, start and stop. That achieves maximum physiological arousal and stress syndrome. And this is the great secret of bullying. Never over do it. Small doses. The victim will do the rest."

Alone in his hotel room at night, Walker poured out his frustration to a video diary, but it didn't help.

"In fact I looked like the crazy one! I thought he was childlike and stupid, but when I look back he was playing me like a violin. And I knew that if I didn't capture any of his tirades on camera I didn't have what I needed for the film."

Just how Walker managed to call checkmate, and escape from Sam Vaknin without sabotaging the film, makes for a thrilling ride. By the end, the film-maker resorts to desperate measures (a shaky secret camera hidden in a backpack), then calls an early end to the shoot rather than spend another day with its main subject.

One area I, Psychopath succeeds strongly is in dispelling the myth that psychopathy is the exclusive domain of serial killers. Experts now believe these dangerous "social predators" are just as common in the stockmarket, the office, halls of industry, houses of parliament, or the corner store.

Perhaps the greatest tragedy of the film is that Vaknin presents as an articulate high achiever who could have traveled a much different path in life if not for his psychopathic traits. His biography reads stranger than fiction. Possessed of a 185 IQ, Vaknin was fast-tracked to university at the age of 11. By 21 he was was flying the world in a private jet. But, in 1997, his world came crashing down when he and his fellow company directors became Israel's first corporate executives to be jailed for insider trading.

He has, by his own admission, made and lost his fortune at least three times. His stint in jail gave him time to reflect, finally coming to the conclusion that the common denominator in all his problems was, in fact, himself.

On his release, Vaknin relocated to Macedonia where he met his wife, Lidija. He now runs an online self-help site for victims of extreme narcissists, operating on the premise that it takes one to know one.

Sam's wife Lidija, an intelligent, yet vulnerable, woman who loves Vaknin despite his abundant selfishness, strikes one of the most heartbreaking chords in the film. When Walker confronts her with footage of "the real Sam" disparaging their relationship it clearly wounds her, yet she is insistent that Sam truly loves her.

"That's exactly how Sam Vaknin fits into all the work I've done before," Walker, explains. "I've always wanted to understand why bad things happen to good people? Why do the good guys so often come last? Why do the bastards always seem to end up with all the fame and money, and every appearance of success?"

"One reason is because psychopaths thrive on good people. It's the one consolation for their victims. They take advantage of people with high empathy, people of goodwill. That's where the evil comes into it."

Professor Bob Hare concurs: "The victims all have something in common and that is that they're human. And everybody can be victimised. I have been victimised, I have been conned and manipulated by psychopaths and I should know better, but how do you know? If we believe in the fundamental goodness of man, we're doomed."

Hare is the recognised world leader in psychopathy research and, as well as his weighty onscreen presence, he agreed to act as the film's scientific consultant. Walker sought him out after reading that, after more than thirty years observing psychopaths inside Canada's high security prisons, the Professor thinks he should have spent more time at the Stock Exchange observing society's more "successful" psychopaths.

In fact, realizing we have all just lived through an era when psychopaths seem to highjack not just capitalism, but democracy, Walker says: "There is a case for using the Psychopathy Checklist to create a kind of revisionist history. Think of Hitler, Stalin, the corporate cheats at Enron, the recently disgraced American businessman Bernie Madoff, even Donald Rumsfeld and the neocon hawks of the Bush era. All have potential to tick most of the boxes.

"It's definitely scary to have looked into the eyes of someone who wants to destroy you," Walker admits. Having survived his brush with a world class psychopath Walker says he has only one real regret.

"I just hope I haven't turned Sam Vaknin into a celebrity psychopath!"