TOKYO - No orders came from any politician for changes to be made to the papers at the heart of a shady land deal to protect Japanese Prime Minister Shinzo Abe, a former bureaucrat who resigned over the deepening scandal told Parliament on Tuesday (March 27).

Former tax agency chief Nobuhisa Sagawa, 60, was head of the Finance Ministry's Financial Bureau when public records were doctored to erase the names of Mr Abe and his wife Akie from 14 documents in a sweetheart deal that has become the prime minister's worst domestic political headache.

Tuesday's hearing was highly anticipated as it was Mr Sagawa's first public statements since he quit on March 9. But he did not provide much clarity in his testimony with a tally by public broadcaster NHK showing Mr Sagawa refused to comment at least 46 times.

His reticence in facing the barrage of questions interrupted the session in Parliament as opposition lawmakers heckled Mr Sagawa and slammed him for being a hostile witness, insinuating that the sitting was a sham that led to more doubts than answers.

While testifying as a sworn witness in the Diet or Parliament means one pledges to tell the full truth, the law allows witnesses to withhold testimony if it is deemed that it may lead to criminal prosecution. Lying under oath, however, is deemed perjury, and is a criminal offence.

"I may be subject to criminal prosecution, so I will refrain from answering," Mr Sagawa replied to questions such as whether he was aware of the identity of the person who had falsified the documents and why.

Several questions remain unanswered. These included who gave the instructions to alter the papers; the motive in tampering with the documents; and Mrs Abe's ties with Moritomo Gakuen, the nationalist school operator at the heart of the scandal.

Former Moritomo chief Yasunori Kagoike, who has been charged for fraud, insisted on Monday that Mrs Abe has been kept abreast of updates throughout negotiations to acquire a plot of land from the government, and had told him to proceed with buying the "good land" in Osaka.

The government had sold the land to Moritomo for only one-seventh of its appraised value to build an elementary school, and Mrs Abe was to be its honorary principal.

Mr Abe has seen his support ratings nosedive more than 10 percentage points across different media polls this month, since the Finance Ministry confessed on March 12 that entire sentences and paragraphs were deleted from the 14 documents.

Protesters on Tuesday gathered outside the Diet , shouting slogans and waving banners. They called for Mr Abe and Finance Minister Taro Aso to step down and not make Mr Sagawa the scapegoat.

Mr Sagawa apologised as he took the stand on Tuesday, saying: "The responsibility for bringing chaos to the Diet and shaking the foundation of the nation's trust in the government falls on me alone."

In his testimony, he also said the fact that Mrs Abe was to serve as honorary principal had "no impact whatsoever" on the deal, and that he did not consult the Prime Minister's Office before he spoke at the Diet last year over the deal.

Lawmakers quizzed him on Tuesday over his prior statements to Parliament, including claims that the documents on the deal were "discarded", or that there had been "no records of any negotiations of the land price or appraised value".

Mr Sagawa said he had testified to the best of his knowledge at the time. He added that he "did not consciously shift answers" because of Mr Abe's vow to resign as Prime Minister and lawmaker if either he or his wife were found to be directly involved in the deal.

Mr Aso, in refusing to heed calls to step down, has alleged that it was a group of wilful bureaucrats who chose to cook the documents on their own accord, wrongly surmising the desires of politicians.

Opposition lawmakers said on Tuesday that they would step up calls for Mrs Abe to be summoned - a move the ruling Liberal Democratic Party (LDP) has strongly been resisting.

Mr Hiroshi Moriyama, chief of the LDP Diet Affairs Committee, said: "Many doubts were resolved and it became clear there was no involvement of Mr and Mrs Abe.

"The whole issue will become clear through the internal Finance Ministry probe and the ongoing criminal investigation. It is unnecessary to summon Mrs Abe because Mr Sagawa's testimony has made it clear that she was not involved."