Malaysian court Friday overturned a 2009 murder conviction for two police officers in a scandal that fascinated the nation and saw critics try to draw a link to Prime Minister Najib Razak.

Azilah Hadri and Sirul Azhar Umar were convicted of the 2006 killing of Mongolian national Altantuya Shaariibuu, a 28-year-old model and interpreter at the centre of allegations of huge kickbacks in a government purchase of French submarines.

"Both the accused have been acquitted and discharged. They are free men now," defence lawyer Hazman Ahmad told AFP.

"Based on the evidence, justice has been done."

Prosecutors said the government would appeal the decision.

Government critics have long alleged that the two men, members of an elite police unit that guards top ministers, were the fall guys in the killing to hide the involvement of their masters at the highest levels of government.

The case stems from charges that Abdul Razak Baginda, a former close associate of Najib, arranged the kickbacks in the $1.1-billion purchase of French Scorpene submarines in 2002.

Najib was defence minister at the time.

Altantuya, who was then Abdul Razak's lover, had reportedly been involved in negotiations over the purchase.

Abdul Razak was later charged with abetting her murder by ordering the two officers to kill her after she allegedly harassed him for a cut of the kickbacks.

Abdul Razak, who is no relation to the prime minister, was acquitted in 2008.

The remains of Altantuya's body were found blown up with military-grade explosives in a jungle clearing near the capital Kuala Lumpur.

Najib has vehemently denied any involvement in the affair, but the corruption allegations have never been fully probed and whispers over the case have continued to dog him.

It was not immediately clear whether the men would be publicly available to comment in the extremely sensitive matter.

The decision triggered an immediate reaction on Malaysian social media, with many calling it part of a widely suspected conspiracy to free the men in return for their silence.

Sirul Azhar has been previously quoted telling a court that he was being "sacrificed" to protect others. But the men are not known to have implicated anyone else.