Former chief of ultra-nationalist education operator Moritomo Gakuen has insisted that Prime Minister Shinzo Abe's wife Akie said a plot of state land in Osaka was "good" and told him to "please push ahead" on a deal.
Yasunori Kagoike, who is facing fraud charges in Osaka, reportedly told opposition lawmakers: "There was 'no mistake' that she said something along those lines and that she received reports from me regarding negotiations to purchase the land."
Kagoike's claims, made last Friday to opposition lawmakers who were granted access by a district judge to interview him while under custody, will probably heighten calls for Mrs Abe to answer questions in Parliament on her role behind the murky land deal.
He also alleged that officials from the Finance Ministry's Kinki Financial Bureau had taken "special interest" in the talks because it involved the Prime Minister's wife.
The raging firestorm has shaken Tokyo's political epicentre Nagatacho, where sizeable protests have broken out almost daily, and threatened Mr Abe's reign in office.
At the crux of the issue is a sweetheart deal, in which state land was sold to Moritomo Gakuen at one-seventh of its appraised value to build a school, with Mrs Abe to be named honorary principal.
The Finance Ministry confessed on March 12 that its Financial Bureau tampered with 14 documents related to the deal to remove all mention of Mr and Mrs Abe. Even entire paragraphs were scrubbed, including one which quoted Kagoike as telling officials that Mrs Abe had told him: "This is a good plot of land, so please move forward."
With the scandal now effectively a he-said-she-said battle, opposition lawmakers are calling for key players in the case to speak under oath in Parliament, or the Diet. Giving false testimony would amount to perjury, a criminal offence.
Former National Tax Agency chief Nobuhisa Sagawa - who was heading the Financial Bureau when the alterations were made between February and April last year - has been summoned to testify in the Diet on Tuesday.
Mr Abe reported to Parliament last Monday that he had asked Mrs Abe about the purported claim, and that she had told him that she said "nothing of the sort".
He has said that he would resign as Prime Minister and lawmaker if either he or his wife were found to have been directly involved.
The ruling Liberal Democratic Party (LDP) insisted Mrs Abe should not have to testify in the Diet, as she is a "private citizen" who has "nothing to do" with the probe into why records were doctored.
But Kibo no To (Party of Hope) lawmaker Masato Imai said on Friday: "Because we don't know to what extent Kagoike's comments are true, it is necessary to question Akie in the Diet."
The opposition may also step up calls for Mrs Abe's former secretary Saeko Tani to testify in the Diet.
Yet within the LDP there are concerns that Mrs Abe's freewheeling ways might come back to bite her husband.
Political observers say the LDP may be hesitant to summon her to the stand, fearing she may cave under intense questioning.
For now, her silence on social media speaks volumes. Previously active on Facebook and Instagram, she has kept mum since March 11. "This time she has to watch herself, for sure," a source close to the government was quoted as saying in a Yomiuri Shimbun report.
LDP chief deputy secretary-general Masahiko Shibayama told public broadcaster NHK that despite Kagoike's claims, there is "no point" in summoning Mrs Abe to the Diet. "The attributions to Mrs Abe in the original pre-altered documents were only assertions by Kagoike."