Stopping short of accusing Dr Mahathir Mohamad of peddling fiction, 1MDB said it prefers to deal with facts.
The firm was responding to his blog post demanding proof that the RM2.6 billion deposited into Prime Minister Najib Abdul Razak's bank accounts did not originate from 1MDB.
The former prime minister also listed a slew of questions for 1MDB, and accused the firm of continuing to mislead the people.
"Unlike Mahathir, who relies on assumptions, 1MDB prefers to deal in facts," the state-owned firm said in a press statement today.
"The retired and former politician has continued to repeat old, unproven and unsubstantiated allegations based on, now he himself admits, assumptions instead of evidence," it added.
"This is despite detailed and factual clarifications being issued by 1MDB and the fact that Mahathir has repeatedly been proven wrong in his claim that ' RM42 billion hilang ' (RM42 billion missing) from 1MDB."
The company said that it is a fact its accounts are audited by reputable, international firms and anyone can easily verify 1MDB facts and figures by reviewing the publicly available audited accounts.
"It is a well-known fact that the auditor-general has been tasked by the cabinet on March 4 to review the past accounts of 1MDB."
It added that an interim report was presented to the parliamentary Public Accounts Committee on July 9 and a final report will be presented to the committee, which comprises both government and opposition MPs on Dec 17
It said 1MDB is and continues to be the most investigated company in the history of Malaysia and it has cooperated fully with the lawful authorities.
'Only Mahathir can be right'
"Documentary proof and evidence has been submitted to these authorities.
"Each of these lawful authorities has independently conducted investigations and publicly issued statements relating to 1MDB."
It said if Mahathir is interested in the truth, he would allow these agencies to complete their investigations and await their findings.
"However, rather than do this, Mahathir continues to freely make unproven allegations without any investigation, without any reference to facts and without any regard to the rule of law and due process."
It said through his statements, Mahathir clearly shows his contempt and disdain of the various agencies that are investigating 1MDB.
"After 22 years in power, in his mind, only Mahathir can be right. This is despite him being proven wrong on ' RM42 billion hilang ' allegation and meekly confessing to not having evidence when asked whether he would lodge a police report against 1MDB," said the company.
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