The public prosecutors offices for the Tokyo, Nagoya and Osaka districts have special investigation squads — elite teams that specialize in the investigation of corruption involving politicians and bureaucrats and large-scale crimes involving enterprises. Unlike other prosecutors, they make arrests as well as prepare indictments.

The arrest Oct. 1 of two senior prosecutors at the Osaka District Public Prosecutors Office’s special investigation squad on suspicion of covering up the alleged destruction of evidence by a subordinate deals a devastating blow not only to the squad but also to the nation’s public prosecution offices, although the two prosecutors deny the allegations against them.

The nature of the alleged crimes by the two is such that people will suspect that something is basically wrong with all public prosecutors even if most are properly doing their work by upholding the principles of investigation.

Prosecutors of the Osaka special squad had indicted a high-ranking bureaucrat over allegations of abuse of the postage discount system for the disabled, but in an extraordinary development May 26, the Osaka District Court rejected 34 out of 43 depositions presented by the prosecution as evidence, pointing to the possible use of leading questions or pressure against witnesses.

On Sept. 10, the court acquitted Ms. Atsuko Muraki, a former bureau chief of the health and welfare ministry. She had been arrested in July 2009 on suspicion of having instructed her subordinate, Mr. Tsutomu Kamimura, to issue a certificate recognizing a certain organization as a benefactor for the disabled, thus enabling it to use the postage discount system.

Then, in a twist of the investigation in this case, the Supreme Public Prosecutors Office on Sept. 21 arrested Mr. Tsunehiko Maeda, the chief prosecutor for the investigation, on suspicion of having changed the time of the last update on a floppy disk seized from Mr. Kamimura from “1:20.06” a.m., June 1, 2004, to “9:10.56” p.m., June 8, 2004.

On May 26, 2009, Mr. Kamimura had been arrested and the floppy disk containing the text of the certificate seized. In the trial, the prosecution argued that Ms. Muraki had instructed Mr. Kamimura to issue the certificate during the first 10 days of June 2004. The court adopted as evidence an investigative report that Ms. Muraki’s defense counsel had obtained from the prosecution. (The prosecution did not submit the floppy disk to the court.) The report mentioned “1:20.06” a.m. (June 1, 2004) as the time of the last update. The defense counsel pointed out that the disk update of shortly past midnight May 31 contradicted the prosecution’s argument. If the prosecution had submitted the altered disk to the court, Ms. Muraki could have been found guilty.

After the floppy disk was returned to Mr. Kamimura in July 2009, its content was found to have been altered. Mr. Maeda reportedly told a colleague that he had “implanted a time bomb in the floppy disk.” The possibility cannot be ruled out that he tampered with the disk to make its content agree with the prosecution’s preconceived scenario.

Mr. Maeda’s arrest was followed by the arrest last week (Oct. 1) of Mr. Hiromichi Otsubo, former head of the special investigation squad, and of Mr. Motoaki Saga, former vice head of the squad by the Supreme Public Prosecutors Office. The office alleges that while the two knew that Mr. Maeda deliberately altered the floppy disk content, they told him in early February to explain to others that he had changed the content by mistake.

The office further alleges that when the two read a written report about the alteration of floppy disk content from Mr. Maeda around Feb. 10, they had him modify the report to make it appear more logical. Therefore, by making the alteration appear to have been a mistake rather than a deliberate act, the office alleges, the two avoided taking legal action against Mr. Maeda, thus shielding him from proper investigation.

Although the floppy disk was not submitted to the court as evidence, the two’s failure to report the alteration to the court or outside authorities seriously violates investigative integrity and betrays people’s trust in fair investigation by public prosecutors and their ethics and professionalism. It is reported that one prosecutor strongly criticized Mr. Saga in person for trying to hide the alteration, and that another proposed to Mr. Otsubo that he disclose the whole story about the alteration. Who could blame people at this point for thinking that such an alteration of a confiscated item by public prosecutors is common practice?

The arrest of the two is not enough to get the total picture of what was going on in the Osaka District Public Prosecutors Office. The Supreme Public Prosecutor Office should find out what kind of information the head and vice head of the Osaka office and the criminal investigation section chief of the Osaka High Public Prosecutors Office received from Mr. Otsubo and Mr. Saga, and to what extent the three grasped the situation. These three officials’ responsibility should be scrutinized and clarified.

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