It would also ratchet up the pressure on Mr Aso, who said he had no intention to step down over the affair, which led to the resignation of the National Tax Agency chief Nobuhisa Sagawa on Friday.
That followed revelations the finance ministry had retained documents that officials had said no longer existed.
The heavily discounted land deal in Osaka involving a school operator at the center of favoritism allegations against Prime Minister Shinzo Abe has drawn renewed attention following a report that relevant Finance Ministry documents were falsified. The emergence of a voice recording cast doubt on Sagawa's claim.
Aso, a close Abe ally, said Sagawa would take a temporary pay cut and might face more punishment.More news: Australia dodges United States metal tariffs after Trump, Turnbull do deal
The death is being reported only a week after local paper Asahi Shimbun reported documents regarding the land sale were manipulated before they were presented to Tokyo's parliament.
Separately, Finance Minister Taro Aso told reporters that another senior official involved in the scandal, Nobuhisa Sagawa, had chose to step down after lawmakers and taxpayers demanded his resignation.
But it is unclear whether the official's death is related to the dubious transaction.
The male official of the Finance Ministry's Kinki regional bureau was found dead on Wednesday at his home in Kobe, western Japan, the sources said, without disclosing other details.More news: Huawei Y9 (2018) With Quad Cameras and Android Oreo Goes Official
Opposition party lawmakers have demanded that Sagawa appear before the Diet to explain the discrepancies. But the Board of Audit of Japan said in November the discount happened because the price was not properly calculated.
The buyers had announced plans to name Abe's wife Akie the honorary principal of a school being built on the same plot.
Prime Minister Shinzo Abe's wife was initially set to be the honorary principal of an elementary school that Moritomo Gakuen planned to open last April. The report alleged some parts of the documents submitted to the Diet a year ago were different from the originals.
The Moritomo scandal pushed Abe's Cabinet approval ratings sharply down last summer, leading to his Liberal Democratic Party's historic defeat in the Tokyo metropolitan assembly election.More news: Protestors are banned from taking action against a Barclays-backed oil pipeline
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