Former American fugitive Marc Rich was a middleman for several of Iraq's suspect oil deals in February 2001, just one month after his pardon from President Clinton, according to oil industry shipping records obtained by ABC News.
And a U.S. criminal investigation is looking into whether Rich, as well as several other prominent oil traders, made illegal payments to Iraq in order to obtain the lucrative oil contracts.
"Without that kind of middleman, the system would not work because the major oil companies did not want to deal with Iraq because there was a mandated kickback," said human rights investigator John Fawcett.
Another broker was New York oil trader Ben Pollner, head of Taurus Oil, who investigators say handled several billion dollars worth of the transactions now under investigation.
Pollner told ABC News he paid no bribes or kickbacks to the Iraqi regime.
Rich is still living in Switzerland and unavailable for comment.
The roles of several American oil companies, including ChevronTexaco and ExxonMobil, are also under investigation. ChevronTexaco received subpoenas requesting information for two separate grand jury proceedings, and said they were cooperating fully with both investigations.
The U.N. oil-for-food corruption scandal only continues to grow in scope. Today, Sen. Norm Coleman, R-Minn., who is leading the congressional investigation into the program, said that U.N. Secretary-General Kofi Annan should resign because the scandal occurred on his watch.
"I think there's a terrible stain on the credibility and the reputation of the United Nations, there's no doubt about that," said Coleman. "If we're ever to get to the bottom, how can you get there if the guy who was in charge during the course of this fraud and corruption is the guy now who is supposed to be ferreting it out?"
Top officials of the United Nations, including Annan, are accused of looking the other way as some $21 billion meant for humanitarian aid was stolen by the Saddam Hussein regime.
Uncovered in the federal criminal investigation were previously undisclosed payments to Annan's son, Kojo, from his employer Cotecna. The Swiss company had been specifically hired to monitor the oil-for-food program.
Annan's son left the company in 1998 but received payments until this year.
Secretary-general since 1997, Annan said this week he was unaware of the payments. "Naturally I was very disappointed and surprised, yes," he said.
Also under criminal investigation is the U.N. official Annan put in charge of the program, Benon Sevan.
Documents discovered by U.S. forces in Iraq suggest Sevan received payments in the form of oil contacts from the Hussein regime, although Sevan has denied any wrongdoing.