Och-Ziff, the American private equity firm, has become the second US financial group to be duped in what is rapidly emerging as one of Japan’s most sophisticated financial frauds.

Och-Ziff is understood to have lost $80 million. Lehman Brothers, the US investment bank, has already been duped out of more than $350 million.

Sources at Japan’s Financial Services Agency told The Times that both the list of victims and the total financial extent of the fraud could be expected to grow further as the police investigation widens.

The alleged fraud is thought to have been devised some years ago and involves arranging large bridge financing loans that are not repaid.

Spokespeople for Och-Ziff Capital Management Group said that the New York-based fund had lost the money in a scam of exceptional complexity and daring in which the head office of one of Japan’s best known companies was used to make a fraudulent transaction appear legitimate.

At the centre of the police investigation is the now bankrupt Asclepius, owned by LTT Bio-Pharma, which was founded by a cousin of the Empress of Japan.

Both Lehman and Och-Ziff believed that they could earn hefty transaction fees – of about $20 million and $5 million respectively – from deals whereby Asclepius would lend money to hospitals for leasing medical equipment.

In the latest alleged scam, it was the apparent role of Marubeni as counterparty to the bridge finance deals that convinced both Lehman Brothers and Och-Ziff that the Asclepius fund, to which they were lending, was above board.

Meetings were held at Marubeni’s imposing head office overlooking the Imperial Palace gardens, and representatives of Marubeni produced legitimate-looking business cards, documents on Marubeni-headed paper and even the critical “inkan” corporate rubber stamps without which no Japanese contract can be signed.

But it has since emerged that the entire process was faked, involved at least one impostor pretending to be a Marubeni director, and that, while some initial payment instalments were met by the fund, the great majority of the money loaned to it has disappeared.

Marubeni admits that the two people who fronted the alleged scam were employees of the company, but that they have since been sacked – a few days, in fact, after the scam first came to light.

Under Japanese corporate law, says Lehman Brothers, a company is responsible for the actions of its employees, and is confident that its efforts to sue Marubeni for the missing $350m will be successful.

Marubeni, meanwhile, has rejected Lehman’s claim, saying that it has no payment obligation whatsoever.

“The case would never have occurred if Lehman had exercised the due care typically expected and required in light of the extraordinary financial amount of the alleged transaction,” the firm said in a press statement.

“The transaction in question was so irregular, and from the amateurish contents of the forged documents, (that) Lehman should have naturally been suspicious,” it continued.

Corporate investigators familiar with the case say that there were several red flags above the Asclepius fund that might have been spotted during periods of due diligence.

These include the fact that Bio-Pharma, the fund’s parent, was on the Tokyo Stock Exchange’s supervisory post for “inappropriate” activities with its stock.

Also suspicious was the fact that Open Loop, a capital partner of Asclepius, was on the supervisory list of the Osaka Stock Exchange for similar reasons.

Lehman Brothers said that the placement of the firms on the exchanges’ watch lists were technicalities.

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