The Serious Fraud Office says it has accidentally sent thousands of pages of evidence relating to an investigation into defence giant BAE Systems to the wrong person.
A statement from the office said it identified the data loss in May and that 98 percent of the material has already been recovered.
The office said that none of the material related to matters of national security.
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Satoshi Uematsu, 26, was sent to the Yokohama District Public Prosecutors Office in Kanagawa prefecture.
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