A MONTH ago, Harry Markopolos was an accountant unknown outside Boston's financial circles.

Now the slight, bookish 52-year-old is under siege. During Christmas week, he spent Monday being interviewed by 60 Minutes, Tuesday preparing to testify in Washington, and Wednesday sorting through pitches from book authors and movie producers. His mother-in-law now answers the door at his suburban stucco house and shoos away the reporters who knock at all hours.

The man who spent nearly 10 years trying to blow the whistle on what appears to be the largest Ponzi scheme in history has achieved a kind of hero status in the investment world. He is poised to reap fame and fortune from a disaster that has cost the investors who relied on Bernard Madoff as much as $US50 billion ($70 billion).

But Markopolos said he was uninterested in co-operating with many of the authors and moviemakers - and feared Hollywood would take liberties with the story. "They'll just add in sex and violence," he said.

Suffering from a cold, he backed out of testifying this week before a congressional committee investigating the US Securities and Exchange Commission's failure to heed his warnings about Madoff. He also felt he was not prepared enough for what would be his first star appearance in public. Now, the floor of his skylit home office is covered with documents and manila folders in which he is organising the papers from his campaign.

Harry Markopolos has never met Bernard Madoff. Instead, he stalked the famous investor through computer analysis of his supposed trading practices and returns. Pennsylvania-born Markopolos moved to Boston in 1991 to join Rampart Investment Management, a firm specialising in the trading of options - contracts that let investors buy or sell stocks and other financial instruments at set prices. Soon, tales of how Madoff was delivering steady profits to clients regardless of market conditions had become a legend - and a mystery - in the investment world.

Markopolos's bosses at Rampart were keen to learn how they could match Madoff's double-digit returns. As the office math whiz, Markopolos was assigned in 2000 to deconstruct Madoff's strategy to see if he could replicate it.

When he couldn't, the task became something of a running challenge around the office.

"I'd say, 'Hey Harry, how come you can't run a program like this?'," said Frank Casey, a former Rampart colleague who now runs a consulting firm for hedge fund investors.

For Markopolos, though, it was no joke. Again and again he could not simulate Madoff's returns, using information he had gathered about Madoff's trades in stocks and options. Madoff seemed to make money whether stockmarkets went up or down, a red flag to Markopolos.

"You can't dominate all markets," Markopolos said. "You have to have some losses." Also, Madoff seemed unusually secretive, even to his own clients - another warning sign.

Markopolos eventually decided Madoff was either running a Ponzi scheme - using money from new clients to pay off old ones - or he was "front running" stocks, improperly trading in investors' private accounts before orders the firm received from outside clients.

Through a Securities and Exchange Commission contact in Boston, Ed Manion, Markopolos began funnelling memos and tips to the agency's New York office, which had jurisdiction over Madoff's company, Bernard L. Madoff Investment Securities LLC.

Despite receiving little response, Markopolos continued to send SEC officials memos and other notes about Madoff, even after he left Rampart in 2004 to start a business investigating financial fraud. His latest communication with the agency was in April, just eight months before the scheme surfaced: in it, he welcomed the SEC's new director of risk assessment to his job with a note about his longstanding concerns about Madoff.

Markopolos allows that he was motivated partly by the possibility of a bounty that the Government pays to whistleblowers in successful prosecutions, if the fraud falls within certain categories. Depending on the size of the fraud, such payments could run into the millions of dollars. But exposing a Ponzi scheme probably would not generate such a bounty.

Over time, Markopolos concluded that he was not likely to get a whistleblower payment, but he continued nonetheless, spurred on by the challenge of cracking a Wall Street legend, as well as continuing encouragement from his SEC friend, Manion.

The culmination of his analysis was a memo Markopolos sent to regulators in 2005 that he titled "The World's Largest Hedge Fund Is A Fraud". It detailed his suspicions and invited officials to check his theories.

"I felt like I was an army of one," Markopolos said recently. "I was a $US50 billion failure. I wasn't good enough or smart enough to outmanoeuvre the SEC, the press wasn't listening to me, and I had no other avenue."

Markopolos is hoping the buzz around him will soon die down so he can resume a low profile. He now works on whistleblower cases, conducting forensic accounting analyses for lawyers who sue companies under the False Claims Act and other statutes, which he said is best done with a certain degree of anonymity.

His wife, Faith, who conducts due diligence of portfolio managers for an investment firm, is of two minds about the attention her husband is receiving. One the one hand, it would be nice to be out of limelight again, she mused. On the other, she said his new-found stature could help his business.

"The next time that the Government sees it's Harry Markopolos bringing something to their attention," she said, "they won't ignore it."

The Boston Globe