KUALA LUMPUR (AFP, REUTERS) - Ousted Malaysian premier Najib Razak is already in hot water over allegations he looted state funds, but his legal woes could worsen as calls grow for a fresh look at an even darker past scandal involving the grisly slaying of a young model.

The lurid earlier affair centred on allegations that Malaysian officials took huge kickbacks in the 2002 purchase of Scorpene submarines from France when Mr Najib was defence minister.

The sensational saga transfixed Malaysia for years until the authoritarian former regime used its leverage to eventually bury it, though whispers persist that Mr Najib, 64, and his wife Rosmah Mansor were deeply involved.

But Mr Najib was trounced in a stunning May 9 election and Malaysia's new government has vowed to investigate not only current allegations that Mr Najib stole billions from sovereign wealth fund 1MDB, but also lift the lid on other unresolved scandals under the graft-plagued former government.

"We are very encouraged by the quick moves so far on (1MDB) and that the government is taking previous corruption seriously," said Ms Cynthia Gabriel, who heads the Centre to Combat Corruption and Cronyism (C4), a Malaysian NGO.

"In this regard, scandals like Scorpene cannot be ignored. Pressure is building and its going to get more interesting."

Mr Najib's immediate concern is allegations that he, his family, and cronies pillaged billions from 1MDB. He is barred from leaving Malaysia and police have seized large amounts of cash, jewels and luxury items from his home and other sites.

But 1MDB pales in many ways to the Scorpene affair, which has sex, submarines, assassins on the run, and an unfortunate Mongolian model and translator.

It centres on allegations that French submarine maker DCNS paid "commissions" of more than 114 million euros (S$180.50 million) to a shell company linked to Mr Abdul Razak Baginda, a close Najib associate who brokered the US$1.1 billion submarine deal.

Mr Najib's opponents said the payments were kickbacks.

Mr Abdul Razak's Mongolian mistress Altantuya Shaariibuu, who was said to have demanded a payoff for working as a translator in negotiations, was shot dead, her body blown up with military-grade plastic explosives near Kuala Lumpur in 2006.

Allegations that Mr Najib and Madam Rosmah were involved in the killing - carried out by two government bodyguards - were steadfastly denied by Mr Najib. He also was forced to publicly deny having had an affair with Altantuya.

The case sank off the radar after a Malaysian court in 2008 cleared Mr Abdul Razak of abetting the murder, sparking allegations of a huge cover-up to protect Mr Najib, promoted to deputy prime minister by then.

But a key figure now looms as a potential game-changer.

Sirul Azhar Umar was convicted along with another police bodyguard in the killing, but he has said they were patsies for "important people" who ordered the murder, and has previously threatened to tell all.

Before he could be jailed, Sirul somehow managed to flee in 2015 to Australia, where he is believed to be in custody.

He told a Malaysian news outlet on Saturday he was ready to reveal who ordered the murder. "I am willing to assist the new government to tell what actually transpired provided that the government grants me (a) full pardon," Sirul, who is in Australian immigration custody, told news website Malaysiakini.

Leading Malaysian politician Anwar Ibrahim, released from jail last week in the wake of the election and who is expected to eventually become prime minister, told AFP on Thursday that Sirul and his accomplice Azilah Hadri should be granted fresh trials.

"At that time, the judiciary was compromised," Mr Anwar, 70, said in an interview.

"I don't know to what extent Najib was involved or not, but he's certainly implicated in some way," he added.

He noted that all traces of Altantuya entering Malaysia before her murder were eliminated, saying that "had to be a higher-up decision".

Also looming is a slow-moving effort in French courts that could reveal more.

French judicial sources last year told AFP that investigators there had indicted two former top French executives linked to the Scorpene deal, as well as Mr Abdul Razak.

Following Malaysia's election, C4 publicly called for an immediate investigation of Mr Najib and others over the submarines and Altantuya's murder, calling the affair "one of the (previous) government's greatest robberies".

Ms Gabriel admits that the sheer backlog of scandals under the former government, including dodgy land deals, looting of timber resources, and numerous suspicious deaths of government critics while in police custody, could delay justice for Altantuya.

Powerful vested interests also remain, including former establishment figures now aligned with the new government.

"It might be tricky. But if they truly are now behind the rule of law, no stone should be unturned," she said.

Dredging up the truth in the Scorpene case can be risky.

In 2008, a private investigator deeply involved in the affair, Mr P. Balasubramaniam, implicated several government officials, including Mr Najib, in the murder. He quickly recanted, later saying he had been threatened, and fled to India.

He returned in 2013 vowing to tell all in the scandal, just as Mr Najib was facing crucial elections, but died two weeks later.

Authorities blamed a sudden heart attack.