Less than two weeks after he was ousted as prime minister of Malaysia by disgruntled voters, Najib Razak faced a four-hour grilling on Tuesday over the corruption scandal that brought him defeat at the ballot box.

In what was only part one of Mr Najib’s statement to the Anti-Corruption Commission, the former leader sought to explain why more than $10m ended up in his personal account from what investigators say was a state-controlled fund.

The US has said that Mr Najib and his associates stole $4.5bn in total from the so-called 1MDB national investment programme, which was supposed to help build public infrastructure in Kuala Lumpur and beyond.

It was the 1MDB scandal that forced Malaysia’s former authoritarian leader, Mahathir Mohamad, out of political retirement at the age of 92. Mr Mahathir headed up the opposition alliance that defeated the ruling coalition for the first time in Malaysia’s post-colonial era.

The commission which questioned Mr Najib on Tuesday is tasked specifically with chasing the 42 million ringgit ($10.6m) transferred into his bank account from SRC International, a former unit of 1MDB, using multiple intermediary companies. Investigators say it will take much longer, and the cooperation of many countries, to pursue an alleged international network of money laundering around Mr Najib.

The former prime minister has strongly denied any wrongdoing, and emerged from the commission’s offices looking calm, and smiling.

He said he had provided “verification of documents and several more complete details” on top of the evidence he gave to a previous investigation into 1MDB, back in 2015.

But the commission also heard from the top investigator in that probe, Mohamad Shukri Abdull, who alleged that he and his colleagues faced threats and intimidation when they came close to bringing charges against Mr Najib.

Mr Shukri fled to the US when the then-attorney general was fired, fearing he was next. One of Mr Mahathir’s first acts as the new prime minister was to sack the attorney general who Mr Najib appointed then, and who cleared him of wrongdoing in 2016.

In emotional testimony, Mr Shukri described how he received a bullet in the post and said he felt guilty for leaving the country as his associates in the agency were removed or transferred.

“We wanted to bring back money that was stolen ... Instead we were accused of bringing down the country, we were accused of being traitors,” he said.

He has now returned as the new chief of a commission tasked by Mr Mahathir with bringing the alleged 1MDB fraudsters to account, as well as recovering any lost money.

In a separate news conference, the new finance minister Lim Guan Eng said the Najib administration had conducted "an exercise of deception" over the 1MDB issue and misrepresented the country's financial situation to parliament.

He said “bailing out” the debt created by 1MDB had already cost Malaysia 6.98 billion ringgit ($1.8 billion), money which he said the Najib government claimed was covered by cost-cutting efficiencies in other ministries.

Mr Najib will appear back before the commission on Thursday, a continuation of a gruelling post-leadership period that has seen his properties raided, with luxury items removed and itemised by corruption police. Both he and his wife have been barred from leaving Malaysia while the graft probe is carried out.

The US Justice Department has previously said it believes $700m from the 1MDB went directly to Mr Najib. In a statement, it said it was looking forward to working with Malaysian law enforcement in investigating the case, adding that “whenever possible, recovered assets will be used to benefit the people harmed by these acts”.