"It's a highly charged matter, politically and emotionally," said Madonsela of the furore caused by her State of Capture report, released after she ended her seven-year tenure in October last year.
Addressing the Cape Town Press Club, Madonsela said the matter had deepened the "trust deficit" in the country, and that a commission of inquiry would clear the air.
"It may well be that the deputy finance minister is not telling the truth," said Madonsela.
Last year, Jonas said he had been offered R600 000 to take the job of finance minister before Nhlanhla Nene was inexplicably removed and replaced by Des Van Rooyen, then a relative unknown.
Van Rooyen was hastily replaced by former finance minister Pravin Gordhan in an attempt to steady the markets and transferred to head the Ministry of Co-operative Governance and Traditional Affairs.
'We need to know'
At the time, Zuma had said that Nene was being moved to help establish a BRICS bank, but the job never materialised.
On Monday, Madonsela said former MP Vytjie Mentor, who claimed to have been offered the job of minister of public enterprises at the Guptas' home in Saxonwold, should also be quizzed.
"She may well be lying, but we need to know if she is lying or not."
She said former government spokesperson Themba Maseko also needed to be questioned over whether he was indeed pressured by President Jacob Zuma and businessman AJ Gupta to give business to the Guptas' The New Age newspaper.
"Again, Mr Maseko may well be lying," she said.
She said that had her former office received enough money to investigate the allegations, the probe would have been over and settled in three months.
'Why was Nene fired?'
The final report was held under lock and key by Parliament until finalisation of an interdict brought by Zuma, Van Rooyen and Mineral Resources Minister Mosebenzi Zwane, who said they had not had a chance to address her concerns.
Madonsela then released an interview she had conducted with Zuma to show that he had been given a chance to respond and that, instead of returning for a meeting to provide further information, he had applied for an interdict against the release of the report.
The report was finally officially released by her successor, Busisiwe Mkhwebane, when the interdict applications were withdrawn.
On Monday, Madonsela reiterated her recommendation that only the chief justice should appoint the commission of inquiry, as the allegations made in the report implicated Zuma as an interested party, and this justified the departure from the constitutional rule that only the president could appoint the commission.
Madonsela was addressing the club's lecture series, An Alternative State of the Nation.
"Why was Nene fired?" asked Madonsela.
"You demystify this matter in a commission."