Portrait not available

Nationality Japanese — commodities / copper / market manipulation / fraud

Yasuo Hamanaka

Documented profile covering 5 controversies, including “1999: Appeal dismissed, eight-year sentence upheld” and “1998: Eight years' imprisonment for fraud and forgery”.

Are you concerned? Right of reply

Profile No. 2133 · Updated on 13 October 2026

5Documented controversies

5Sources

1 followed by a conviction

§ Legal statuses reflect the documented sources as of the date shown; they replace neither court decisions nor the presumption of innocence. Counts are not a rating. Methodology

I. Documented controversies

Case · 4 documented stages

1999: Appeal dismissed, eight-year sentence upheld

Conviction

25 June 1999

1999: Appeal dismissed, eight-year sentence upheld

Conviction

The Tokyo High Court dismisses Hamanaka's appeal and upholds his eight-year sentence, refusing to treat Sumitomo's control weaknesses as sufficient grounds for a reduction.

State of the evidence: Documented

Sources · 1

[1]
The Japan TimesHigh Court rejects copper trader's appealPressHigh reliability

Last verified: 14 September 2026

Add to this entry

26 March 1998

1998: Eight years' imprisonment for fraud and forgery

Conviction

Tokyo District Court sentences Hamanaka to eight years in prison for fraud and forgery related to concealing his transactions and Sumitomo's losses.

State of the evidence: Established by a court
Attribution: Accused

Sources · 1

[1]
The Washington PostFor the Record — Yasuo Hamanaka sentencedPressHigh reliability

Last verified: 14 September 2026

Add to this entry

1996–17 February 1997

1996–1997: Forged signatures and $770 million fraud against Sumitomo subsidiary

Conviction

Japanese prosecutors accused Hamanaka of forging superiors' signatures and defrauding a Hong Kong subsidiary of Sumitomo of approximately $770 million to conceal losses. He pleaded guilty at the opening of his trial.

State of the evidence: Established by a court
Attribution: Accused

Sources · 1

[1]
Los Angeles TimesTrader Pleads Guilty in Sumitomo ScandalPressHigh reliability

Last verified: 14 September 2026

Add to this entry

1985–June 1996

1985–1996: Decade of unauthorised copper positions and losses reaching approximately $2.6 billion

Conviction

For years, Hamanaka undertook unauthorised copper trades that ultimately cost Sumitomo approximately $2.6 billion.

State of the evidence: Documented
Attribution: Directly implicated

Sources · 1

[1]
The Japan TimesRogue copper trader draws eight-year prison termPressHigh reliability

Last verified: 14 September 2026

Add to this entry

October 1995–June 1996

1995–1996: Strategy of dominant positions and manipulation of global copper market

Civil / administrative proceedings

The CFTC described a strategy implemented through Sumitomo and Hamanaka to acquire dominant positions and keep copper prices and spreads artificially high.

State of the evidence: Documented
Attribution: Directly implicated

Sources · 1

[1]
U.S. Commodity Futures Trading CommissionCFTC Files and Settles Action Against Sumitomo Corporation for Manipulating the Copper MarketRegulatory authorityVery high reliability

Last verified: 14 September 2026

Add to this entry

II. Constellation of documented links

No documented link with another published profile for now.

Two profiles are linked when a documented controversy of one names the other. The link points to that controversy and its sources; it does not indicate a personal relationship.

III. Has something changed?

A new court decision, a missing source, a mistake? Tell us what should be updated: every request is read by the editorial team.

Support the archive

Controversia checks and updates its profiles independently. Support is optional and has no effect on the content of profiles.

Donate