This story was first published on March 1, 2009. It was updated on June 10, 2009.

Later this month, Bernard L. Madoff will be sentenced for what is believed to be the largest financial fraud in history. He will most likely spend the rest of his life behind bars. Yet there is still much we don't know about the scam, which involved by some account a fraud of more than $50 billion. Investigators are still trying to figure out who all was involved and where the money went.

But the proof that it happened can be found in the ruined lives of thousands of victims. The one person who knows the most and is willing to talk about it is Harry Markopolos, the man who figured out Madoff's scheme before anyone else.

Markopolos sat down with 60 Minutes correspondent Steve Kroft earlier this year for his first television interview .

Until a few months ago, Harry Markopolos was an obscure financial analyst and mildly eccentric fraud investigator from Boston who most people would never notice on the street.

But today he enjoys an almost heroic status, pursued by journalists and movie producers, and honored by colleagues as the man who went to the Securities and Exchange Commission and blew the whistle on Bernie Madoff and his $50 billion fraud.

But he seems uncomfortable with the attention, and knows that he is no hero. "I stand before you a 50 billion dollar failure," he said at an event.

Asked how many times he sent materials to the SEC, Markopolos told Kroft, "May 2000. October 2001. October, November, and December of 2005. Then again June 2007. And finally April 2008. So five separate SEC submissions."

"And in spite of all of the things that you did, it still ended up in disaster?" Kroft asked.

"There's nothing to be proud about in this case. I feel horrible about the result. It's been a total disaster for the victims," Markopolos replied.

It began a decade ago, when Markopolos was working for a Boston investment firm. His boss told him that Madoff, a former chairman of the NASDAQ stock exchange, was running a huge unregistered hedge fund that was producing incredible returns. He wanted Markopolos to reverse-engineer its trading strategy and revenue streams so the firm could duplicate Madoff's results.

"He had the patina of being a respected citizen. One of the most successful businessmen in New York, and certainly, one of the most powerful men on Wall Street. You would never suspect him of fraud. Unless you knew the math," Markopolos told Kroft.

"I mean, you're like a math guy, right?" Kroft asked.

"I've taken all the calculus courses, from integral calculus through differential calculus, as well as linear algebra. And statistics, both normal and non-normal," Markopolos said.

Asked how long it took him to figure out something was wrong, Markopolos said, "It took me five minutes to know that it was a fraud. It took me another almost four hours of mathematical modeling to prove that it was a fraud. "

It was the performance line that Markopolos said caught his attention. "As we know, markets go up and down, and his only went up. He had very few down months. Only four percent of the months were down months. And that would be equivalent to a baseball player in the major leagues batting .960 for a year. Clearly impossible. You would suspect cheating immediately."

"Maybe he was just good," Kroft remarked.

"No one's that good," Markopolos said.