Among the many former and serving White House officials who accompanied President Bill Clinton on his final, triumphal, visit to Belfast on December 13th was Jack Quinn, a lawyer and former chief of staff to Vice-President Al Gore.

Mr Quinn had every reason to join in the celebrations, having played a supportive role in the peace process, but he had other things on his mind that evening. As a Van Morrison recording of Brown Eyed Girl filled the hall, Mr Quinn collared White House counsel Bruce Lindsay and asked him to take a look at a pardon request that he had sent to the President two days earlier, and to make sure that Mr Clinton saw it.

The pardon application was for 66-year-old Marc Rich, a fugitive commodities trader alleged by US prosecutors to be the biggest tax evader in US history. Mr Rich, along with his business partner Pincus Green, had fled from the United States in 1983 to escape prosecution for tax evasion and illegal oil trading, and is today living in Switzerland.

Mr Quinn had been hired by Mr Rich to press the case for his free return to the United States. The former White House official had seized the moment in Belfast, according to the Washington Post, to make a pitch to Mr Clinton as time ran out on the President's final term.

Mr Rich was the most high-profile white-collar fugitive on the FBI wanted list and was once regarded as the most brilliant, if also the most avaricious, commodities trader on Wall Street. He began his career in the 1950s with other European Jewish immigrants in Philipp Brothers commodities firm, before branching out on his own.

In the 1970s, he negotiated many complicated trades in oil and metals all over the world, often rushing in where other brokers feared to trade. This became his downfall. After his company made $100 million by selling oil above the government-controlled price through Swiss-based companies, he came under investigation by prosecutors in the office of New York US attorney, Rudi Giuliani. In 1983, he was charged with 51 counts of tax evasion, racketeering, conspiracy, mail fraud and wire fraud.

Mr Rich was also accused of trading with the enemy, as his companies had purchased crude oil from Tehran at a time when trade with Iran was banned.

Mr Rich was defended by lawyer Edward Bennet Williams, who offered prosecutors a deal. The trader would pay a $100 million fine as long as he stayed out of jail. However, the plea offer was refused and Mr Rich suddenly disappeared overseas rather than face a New York court.

Mr Bennet, in disgust, accused him of spitting on the American flag and the jury system. A judge froze Mr Rich's assets and a year later two of his companies pleaded guilty to criminal charges and paid $200 million in fines. Mr Giuliani framed the $200 million cheque and hung it in his office.

The soft-spoken trader with hooded eyes and a fondness for good cigars took up residence near Zurich with his wife Denise Eisenberg, a New England heiress and daughter of Holocaust survivors, with whom he had three daughters.

From there he continued his trading, mainly in oils and metals. Fluent in English, French, German and Spanish, he conducted business all over the world, even with the US government, to which he sold $45 million worth of nickel and copper for making coins. Denise Rich became a successful songwriter, winning a Grammy nomination.

It was a lavish but perilous exile, with elements of a John le Carre novel.

Mr Rich hired private security guards from Israel for round-the-clock security, ever fearful of a kidnap attempt by bounty hunters seeking a $750,000 US reward for his capture. New York police commissioner Howard Saffir went to Switzerland to try to trap Mr Rich, but his plot was uncovered by the Swiss police.

"He had tremendous sources of information in the Swiss government in a lot of governments," said Saffir, who described Mr Rich as someone who considered himself "a citizen of the world, inconvenienced by the laws of nations".

Though he lived in a five-bedroom mansion full of valuable art works, including two Picassos, and was honoured with invitations to the World Economic Forum in Davos, Mr Rich apparently felt his exile acutely, especially when he was unable to attend the funerals in the US of his father and a daughter who died of leukaemia aged 27.

From the moment he fled, Mr Rich conducted a legal battle to clear his name and get back to the US. In 1984 he hired a former Nixon counsel Leonard Garment, who recruited a leading tax lawyer Martin Ginsburg and Harvard tax specialist Bernard Wolfman to look at his case. They concluded that Mr Rich did not owe any taxes, partly because unreported profits in his Swiss companies were not subject to US taxes.

Despite offers of a $100 million settlement, prosecutors refused to drop the case. "It was never about money. If the biggest tax evaders in the US never did jail time, we could never prosecute another tax case," said Morris Weinberg, who led the prosecution with Mr Giuliani in 1983.

A lawyer for Rich pleaded again with New York prosecutor Patrick Fitzgerald for a deal in 1994.

Mr Fitzgerald said: "If your clients genuinely believe they have done nothing wrong, they should board the next plane to New York and subject themselves to the jurisdiction of the court."

When Jack Quinn took up the case in 1999 with Mary Jo White, currently the New York prosecutor, he was, as he put it, "shown the door". Negotiating with fugitives, said her office, would give defendants an incentive to flee. A pardon, he realised, was the only option left.

The commodities trader had by this time many friends in high places. During his fugitive years, Mr Rich spent an estimated $200 million in philanthropy. In Israel he financed the resettlement of Ethiopian and Soviet Jews and funded hospitals and museums. In Switzerland he bankrolled hockey teams and an organisation which trained sniffer dogs. He funded an eye clinic in Zimbabwe and the 1988 Jamaican Olympic bobsled team.

Israeli prime minister Ehud Barak found time to call Mr Clinton twice in early January on Mr Rich's behalf, emphasising his charitable role in Israel.

Many other prominent Israelis spoke up on behalf of the trader who was born Marc David Reich in Belgium in 1934, and came to New York with his family when they fled from the Nazis in 1941. They included Nobel Peace prizewinner Shimon Peres and Jerusalem mayor Ehud Olmertt.

Some glowing testimonials were obtained from institutions like the Sacred Heart University in Connecticut, which did not know they would be included in the pardon application.

Mr Rich also received support from an unlikely ally, his ex-wife Denise whom he had divorced to marry his second wife, Gisela Rossi. Denise Rich had become one of New York's top fund-raisers and a Democratic Party socialite.

She raised $4 million for the president just after the publication of the Star report, and gave $70,000 in soft money to Hillary Clinton's successful Senate campaign. Wearing a dress showing a deep cleavage, Denise was photographed with singer Michael Jackson and Bill and Hillary Clinton at a cancer benefit last autumn.

Despite her initial bitterness at the split-up - she said Mr Rich showed his thanks for her support "by cheating on me with another woman and publicly humiliating me and my children" - she also lobbied the president for his pardon.

Just hours before leaving the Oval Office for good on January 20th, Mr Clinton pardoned 170 people. Among them was Marc Rich, much to the disgust of the prosecutor's office.

The president said he had been swayed in Mr Rich's case by the decade-old finding of the tax experts, and Jack Quinn's assertion that "I believe in this cause with all my heart". Mr Rich can now return to the US whenever he chooses.