Home Minister Ahmad Zahid Hamidi has been asked when he said he was prepared to extradite Malaysians to Thailand over the 1MDB-Petrosaudi case, if it would include former prime minister Dr Mahathir Mohamad.

DAP supremo Lim Kit Siang raised this amid rumours that Mahathir's aide may be sought to facilitate the case against former PetroSaudi International (PSI) staff Xavier Andre Justo.

Thai authorities on Monday arrested Justo for allegedly blackmailing his former employer by threatening to release information he purportedly stole from the company.

"Imagine Mahathir as a traitor hand-in-glove with Justo to tamper with leaked information?

"I wonder whether Zahid was thinking of the country’s fourth prime minister when he toyed with the idea of 'extraditing' Malaysians to Thailand to facilitate the Thai police in their interrogation of Justo," said Lim in a statement today.

Mahathir is Prime Minister Najib Abdul Razak's fiercest critic on the latter's handling of 1MDB, which had accumulated a massive RM41.8 billion debt which it is now struggling to repay.

PSI's leaked information, which included its communications with 1MDB, had put the latter in a spot as it revealed questionable fund transfers to a company allegedly controlled by Malaysian billionaire Jho Low, who is close to Najib's family.

'Smelling a rat indeed'

Zahid claimed that Justo had admitted during interrogation by Thai authorities, that Malaysians had purportedly asked him to tamper with the information he is said to have stolen, which was subsequently passed to whistleblower website Sarawak Report.

This is despite a senior source in the Thai police telling Malaysiakini that Malaysian authorities are not involved in the probe, and that the case against Justo focuses on the blackmail allegation.

Lim described Putrajaya's offensive as "The Empire Strikes Back" after months of relentless attacks by Mahathir, which has weakened Najib's government.

"I have never heard of the existence of Justo until news reports of his arrest in Thailand, but nobody really believes that his arrest would be able to save Najib and 1MDB.

"I dare say that the overwhelming majority of Malaysians agree with Mahathir that Justo’s arrest was 'suspicious and appears planned', and that 'very clever propagandists were hard at work'," he said.

Lim pointed out that despite claims that the leaked PSI information was tampered with to put 1MDB in bad light, the police report lodged by PSI in UK was about "stolen emails" and not falsified information.

He added that Putrajaya should show proof if it insists that the information was tampered with.