Irish businessman Paul Murphy, who was convicted by a court in Switzerland of laundering £5 million (€6.35 million) in drugs money last month, has claimed the case against him hinged on "incomplete information" and "surmise".

Speaking for the first time from La Stampa jail in Lugano, Murphy (40) protested his innocence. He claimed he had been the fall guy, the victim of a string of unfortunate coincidences, an over-zealous prosecutor and not least his own naivety and stupidity.

He was jailed for six years for two counts of money laundering and one of embezzlement. Having served more than two years on remand, he will probably spend another two years in jail.

He alleged the case - billed in Switzerland as one of its biggest money-laundering trials - hinged on incomplete information, surmise and "a misunderstanding of the nature of trade financing" in his specialist field. He added that he would clear his name once he was free.

"I am innocent of the drugs charges and when I get home I'll be able to prove this beyond any shadow of a doubt."

He said he was now looking forward to studying maths and philosophy, but regretted he could not be with his wife, Carol, his parents, and sister Belinda.

Following a series of high-profile scandals over millions of pounds deposited in Swiss banks by corrupt political regimes, Switzerland brought in tough new legislation in 1998 to crack down on money laundering.

To prove a case is difficult and involves establishing that funds were the proceeds of a crime usually committed abroad and that the person involved was aware of this criminal origin.

Public prosecutor Ms Maria Galliani admitted the case against Murphy was based on "indications that make up a larger picture" and not concrete evidence. But she said this was enough and described Murphy as an "extremely dangerous and unscrupulous criminal" and demanded 15 years' jail in respect of the drugs trafficking, money laundering and embezzlement charges.

The court concluded that some of the dirty money must have been from drugs, but it threw out the more serious charge of drugs financing or trafficking, concluding that Murphy had not been working directly for Colombian cocaine barons but for their middlemen.

Murphy denied handling drugs money via an American client, Todd Faught, who was convicted of money laundering in Miami a year after they first started doing business in late 1997.

Murphy said he terminated the relationship after five months and produced a copy of the charge sheet in the Miami trial to show there was no mention of drugs.

But the court in Lugano, in which the case against Murphy was heard, ruled a drugs link was likely.

The other source of drugs allegations was a US Drugs Enforcement Administration report in which an anonymous informant alleged Murphy and Faught laundered drugs money.

Murphy's trial heard that he and a former business associate, Irishman Mr Tom Forde, were trustees of an Irish-registered trust - the Hibo trust - into which a German company executive deposited £4.8 million (€6 million) in 1997. Later, the executive was convicted of embezzling company money.

The money was transferred to an account at Citibank in New York held by a Colombian bank, Banco Andino. But it was mysteriously rerouted to Banco Andino in Cartagena to an associate of Faught and never seen again.

Murphy was accused of embezzling this money. The court, however, convicted him of only taking about one-fifth of it - something he also denies.

Dublin-based Mr Forde, who said he had done very little business with Murphy, was asked to attend the trial to give evidence and was offered immunity from prosecution while doing so. But he declined to travel to Switzerland, saying he was unwell.

Mr Forde confirmed that he had assisted the US Drugs Enforcement Administration in its action against Faught. Prosecutors from Switzerland travelled to the US to observe the case and noted Mr Forde's evidence.

"I have many questions for Mr Forde. I find his behaviour very upsetting," Murphy said.

Murphy admits he acted incorrectly but protests his innocence. His main regret is that he was "not the best judge of character" and trusted the wrong people. When asked how so many of his associates turned out to be dishonest, he said it was "bad luck".

Although he admits to having earned £450,000 from about 47 transactions, he says it was "not as much as prosecutors said it was" and denies being so dazzled by huge commissions that he omitted to observe the basic rules of business.

"There were many impressive people. Of course one of the first rules of business is to know your customer, but when you're busy you tend not to take the time to do all the checks. In this case I was very remiss. I can't justify it. I was stupid, really stupid," he said.

Murphy described jetting around the world over the past decade to countries often stigmatised by corruption where few consultants were prepared to work - to "help clean business people" import goods into their countries.

It was his dealings with Faught and, in turn, the Colombian clients Faught introduced him to in 1998, that got him into trouble.

Murphy said he created schemes for the Colombians to purchase goods abroad by securing short-term dollar loans in the US to buy goods, such as shoes and tyres, and import them into Colombia. It was a way of coping with the highly fluctuating peso currency.

Some loans were provided by Faught, whom Murphy met initially to help with refinancing a dredging company, but soon afterwards to provide his Colombian clients with short-term loans to purchase goods for importation.

Faught turned out to be "unreliable" and Murphy said he started working directly for the Colombians. But in the absence of Faught, they needed to find someone else prepared to put up large sums of money. Murphy had a client, a mysterious Italian clergyman, whom he first met off a private jet at Frankfurt airport in 1996.

"He was presented to me as a very wealthy individual who represented powerful groups in Italy and wanted to retain anonymity. Private individuals don't like to give all their details," he said, adding that he had been highly recommended as a clean and respectable individual.

The Italian later introduced him to an unnamed English client and both agreed to provide highly leveraged loans for the Colombians. He never asked their identity.

Prosecutor Galliani rejected Murphy's explanation and accused him of funnelling drugs money for Colombian drugs barons through a complex web of accounts in Europe, north and south America, and the Middle East to disguise its criminal origins. She said Faught, the Italian and English clients were middlemen in the employ of Colombian drug barons.

"Whether naivety or stupidity, I should not have gone along with it but I was so absorbed in doing something so helpful for other people. It's a very demanding job but extremely stimulating, it was a challenge. I succeeded where others couldn't and achieved results. It was a tremendous buzz," Murphy said.