Public prosecutors have questioned former Finance Ministry bureaucrat Nobuhisa Sagawa on a voluntary basis over the ministry’s falsification of documents related to the controversial discount sale of state land to school operator Moritomo Gakuen, informed sources said Monday.

The special investigation squad of the Osaka District Public Prosecutor’s Office is believed to have sought an explanation from Sagawa about his possible involvement in document tampering and other relevant matters to the deal, according to the sources.

Sagawa was director-general of the Financial Bureau at the ministry’s headquarters in Tokyo when documents were altered between February and April 2017, shortly after the questionable sale to Moritomo Gakuen in the city of Toyonaka, Osaka Prefecture, came to light.

A criminal complaint has been filed against Sagawa, including suspicion of falsifying public documents.

The investigation squad has already questioned officials from the Financial Bureau, which is in charge of the management of state-owned assets. It has also talked to the ministry’s Kinki Local Finance Bureau, which covers a region that includes Osaka Prefecture.

The prosecutors are expected to judge whether it is possible to build a case against Sagawa by comparing his answers to statements given by ministry and bureau officials, the sources said.

The ministry has said that the documents in question were altered so that there would be no contradictions between their content and what Sagawa said about the deal in the Diet last year.

According to investigative sources, some Finance Ministry officials said during voluntary questioning that the Financial Bureau instructed the Kinki bureau to alter the documents through means such as email.

During his sworn Diet testimony on March 27, Sagawa refused to comment on whether he was involved in the tampering.

He resigned as commissioner of the National Tax Agency last month to take the blame for the confusion created by his 2017 parliamentary remarks about the land deal.

The ministry has been found to have falsified 14 sets of documents. Specifically, it removed or changed descriptions about the negotiation process with Moritomo Gakuen and remarks containing the name of Akie Abe, the wife of Prime Minister Shinzo Abe.

Akie was once named honorary principal of an elementary school that Moritomo Gakuen planned to set up on the plot of land in question. The building plan was canceled after the school operator came under fire over the controversial deal.

At a parliamentary meeting earlier this month, Mitsuru Ota, the incumbent director-general of the Financial Bureau, admitted that the ministry had asked the Moritomo Gakuen side to lie about the plot of land by saying that thousands of trucks were used to remove waste buried at the site.

The land was valued at ¥956 million but was sold to Moritomo Gakuen for ¥134 million in June 2016.