Michael Woodford, former CEO of Olympus Corp, blew the whistle on the scandal after he was sacked [Reuters]

An investigative panel has found no link to organised crime in the accounting scandal at Japan's Olympus and has blamed two former executives for cooking its books over the past 13 years.

"As of a result of our investigation we were unable to find any evidence of the company's money being sent to members of organised crime," Tatsuo Kainaka, the panel's head, said on Tuesday.

In its report, the panel described Hisashi Mori, Olympus' former executive vice president, and Hideo Yamada, ex-internal auditor, as part of a management team that was "rotten", adding that "parts around it were also contaminated by the rot".

The two crafted a scheme as long ago as 1998 to hide investment losses from corporate stakeholders, the report said.

The concealment of losses amounted to $1.73bn at the peak of the cover-up, though the panel felt it would have been difficult for then-auditor KPMG AZSA to spot.

The panel's findings so far represent no major new surprise for investors, with the camera and medical equipment giant having already admitted to hiding substantial investment losses for two decades and having named three former executives as the main wrongdoers.

Some doubts exist, however, about the ability of the panel to get to the bottom of such a complex case, which involves numerous counterparties and investment firms.

The panel has limited powers of investigation and was hired by the same board that sacked Michael Woodford, the former CEO who blew the whistle on the scandal immediately after he was dismissed in October.

"I would have thought they didn't have the expertise to probe that [involvement by organised crime]," said Jamie Allen, secretary-general of the Asian Corporate Governance Association, whose members include institutional investors that collectively manage assets of more than $10tn.

"That's really a job for the police. So even if they say there's no evidence, obviously I don't think that's going to satisfy everybody because they'll want to know what the police come up with."

Market rebound

Olympus has lost half of its market value since Woodford raised concerns over murky accounting and some expensive and questionable acquisitions.

But the company's stock jumped as much as 15 per cent on Tuesday, extending a three-week rally fuelled by growing hopes that Olympus would not be delisted and that, instead, a few former executives would bear the brunt of any punishment.

"I think the probability for Olympus to be kept as a listed company is pretty high right now and that's the market consensus," said analyst Nanako Imazu of CLSA.

Olympus must clear a series of hurdles to avoid being delisted, a humiliation that could force it into asset sales.

The first of these challenges was for the panel to find no involvement of organised crime in the company's scandal.