Najib has consistently denied any wrongdoing related to 1MDB since the scandal erupted in 2015, and has said $681 million of funds deposited in his personal bank account were a donation from a Saudi royal.
Embattled former Prime Minister Najib Razak arrived at the headquarters of Malaysia's anti-corruption commission on Tuesday, which has ordered him to explain a suspicious transfer of $10.6 million into his bank account.
The sum is just a fraction of billions of dollars allegedly siphoned from state fund 1MDB, a scandal that dogged the last three years of Najib's near-decade-long rule and was one of the main reasons why voters dumped him in an election on May 9.
That shock election result upended Malaysia's political order, as it was the first defeat for a coalition that had governed the Southeast Asian nation since its independence from colonial rule in 1957.
Since losing power, Najib and his allegedly shopaholic wife, Rosmah Mansor, have suffered a series of humiliations, starting with a ban on them leaving the country, and then police searching their home and other properties.
Flanked by security guards, Najib entered the Malaysian Anti-Corruption Commission (MACC) headquarters in Kuala Lumpur on Tuesday, moving slowly through a throng of journalists outside the building. Wearing an open-neck shirt, Najib looked relaxed and smiled once he entered the building's atrium.
TRT World's Alican Ayanlar has more.
Finding out what happened to billions of dollars that went missing from state-investment fund 1Malaysia Development Berhad (1MDB) is a priority for Malaysia's new leader, Mahathir Mohamad, who at the age of 92 came out of political retirement and joined the opposition to topple his former protege.
New MACC chief Mohd Shukri Abdull told reporters to expect a "special briefing" on Tuesday.
Najib has consistently denied any wrongdoing related to 1MDB since the scandal erupted in 2015, but he replaced an attorney-general and several MACC officers to shut down an investigation.
Najib has said $681 million of funds deposited in his personal bank account were a donation from a Saudi royal, rebutting reports that the funds came from 1MDB.
Now answering to a different prime minister, the MACC has reopened its investigation, initially focusing on how 42 million ringgit ($10.6 million) went from SRC International to Najib's account.
SRC was created in 2011 by Najib's government to pursue overseas investments in energy resources, and was a unit of 1MDB until it was moved to the finance ministry in 2012.
Mahathir's office also announced the establishment of a new task force made up of members of the anti-graft agency, police and the central bank, which would liaise with "enforcement agencies in the United States, Switzerland, Singapore, Canada and other related countries," investigating 1MDB.
The US Department of Justice refers to Najib as "Malaysian Official Number 1" in its anti-kleptocracy investigation into 1MDB.
Addressing loyalists in his home state of Pahang on Sunday, Najib declared: "I did not steal from the people".
He said the chorus of allegations was a smear campaign aimed at ruining the United Malays National Organisation, the party that until now has led every government since Malaysia's independence six decades ago.
Police were filmed taking away at least 284 boxes of potential evidence, notably jewellery, cash, designer clothes and accessories. The publicity given to the search prompted Rosmah to issue a statement through her lawyers complaining of the danger of a "premature public trial".
Speaking to staff at the prime minister's office on Monday, Mahathir counted the cost of his predecessor's alleged misgovernance.
"We find that the country's finances, for example, was abused in a way that now we are facing trouble settling debts that have risen to a trillion ringgit," he said.
The previous evening, Mahathir met Xavier Justo, a Swiss national who was the first whistleblower in the 1MDB affair. Justo posted a photograph of himself with Mahathir on his Facebook account.
It was documents leaked by Justo, a former director of energy group PetroSaudi International, which ran an energy joint venture with 1MDB from 2009 to 2012, that triggered investigations in at least six countries.
Justo was sentenced to three years in prison in Thailand in 2015 on charges of blackmail and attempted extortion after what he now says was a confession made under pressure. He was freed in an amnesty in 2016.
SRC came into focus after the Wall Street Journal reported that funds from the company were transferred using multiple companies as fronts, before eventually reaching Najib's account.
As these funds were moved through Malaysian, rather than foreign, financial institutions it was easier for MACC investigators to establish the money trail.