It started out as a skerrick of vague information: an unidentified foreigner, probably an Australian, had been arrested in eastern India after sexually abusing boys at an orphanage.

Months of investigation later, ABC South Asia correspondent Sally Sara has pieced together the full story: a disturbing and bizarre account of Paul Henry Dean, an Australian businessman who dumped family, friends and middle class comforts for a new life among lepers, orphans and the desperately poor of India.

Dean donned an array of names and identities while he operated as a charity worker, masqueraded as a holy man and a healer, and allegedly abused dozens of boys and young men in his wanderings over 30 years.

But the story starts far from the chaos and deprivation of India.

Across the Indian Ocean, in the serene WA beachside city of Bunbury, locals say they remain mystified by the man who grew up among them.

In the 1960s and 1970s Dean was seen as a smart young man on the make - "a go-getter", full of money-making schemes and big ideas.

He revived the local Young Liberals and won the presidency of the local surf club - a tribute more to his organisational ability than to his surf prowess, club veterans say.

One summer night in 1976 he threw a party, then suddenly vanished. At first, foul play was suspected. But police discovered that he had left the country on a fake passport. More than $100,000 was missing from the travel company he had chaired. It was thought he had fled to the UK, or Indonesia.

But Dean was living among Catholic missionaries in an ashram in southern India, calling himself "Brother Alan" and claiming to have been a professor of agriculture in Australia.

He travelled the countryside pretending to be a Catholic brother and a priest. He even said Mass for Mother Teresa's missionaries.

He watched local doctors at work and quickly learned to copy them. Establishing himself in leper colonies in eastern Andhra Pradesh and Orissa states, Dean signed letters as "Dr Bro Paul," and began performing cataract operations and limb surgery, including amputations, on lepers.

He became, in the words of a former mayor, "a walking god", admired for his intellect, feared for his quick temper.

"He could have been Mother Teresa, he could have been Hitler," says Nathalie Nellens, a young Belgian volunteer who saw Dean at work.

At Titlagarh in Orissa in the early 1980s, Dean surrounded himself with teenage boys who were keen to learn paramedical training and build themselves a future.

Titlagarh is fiercely hot, remote and impoverished. Most of the former trainees, now men in their 40s, are still there. Despite the passage of time their memories are vivid. Dean, they say, had repeatedly used them for sex. They had complied because they were young and poor and felt they had no choice. On camera they describe in uncomfortable detail what happened to them. This is the first time their stories have been told.

The accounts from these men at Titlagarh provided the earliest known evidence of Dean abusing boys. It was to become a pattern. Dean operated with impunity, moving into charities that worked with orphans. He adopted the benign nicknames "Professor", or "Tata", meaning grandfather.

"Tata tells me to put oil on his penis and hand-pump him. He also undresses me and masturbates me. This has been going on since 2005. He threatened to beat me up if I told...", a teenage boy said in one of at least eight statements by teenage boys to police in 2008.

So far Dean has deftly eluded accusations of abusing boys. The children's charities where he has worked as a trusted volunteer have mostly accepted his denials.

Frenchwoman Mary-Ellen Gerber, who founded an orphanage near the city of Puri in eastern Orissa, says she twice put allegations of sexual abuse to him and both times he tearfully protested his innocence.

She now regrets backing him.

Dean has also kept authorities at bay. In 2001 he was arrested and charged with sex and passport offences. Eight years later those charges have not been to trial. Now he is facing another set of charges in another state. He denies all the allegations against him.

Australian authorities have known of the allegations but have shown no inclination to act against the man who fled Australia more than 30 years ago on a fake passport, wanted for theft, and who has roamed India ever since.

Dean has mostly been someone else's problem, changing countries, moving from state to state, from one charity to another.

No one has put his story together - until now.

-Sally Sara's report airs on Four Corners tonight on ABC1 at 8:30 pm.