Prime Minister Najib Abdul Razak and his government have a duty to clear the nation's name regarding the murder of Altantuya Shaariibuu, Dr Mahathir Mohamad says.
"Proof must be given that the murder, 'cover-up', police involvement and (Abdul) Razak Baginda were in no way guilty of the terrible crime.
"The judiciary including the Attorney General's Chambers too must clear their names, especially with regard to the acquittal of Razak Baginda ( photo ) and the appeal by the attorney-general, which was confined only to the two policemen.
"They were retried and were found guilty and sentenced to be hanged to death," Mahathir added in a blog post.
The former prime minister was commenting on the Al Jazeera documentary about the slaying of the Mongolian national, titled 'Murder in Malaysia'.
Mahathir said Malaysians abroad are already being asked what has happened to their country, and this latest episode would worsen the situation.
"The government must take this documentary film seriously and try to clear our name.
"Taking it (the documentary) off Al Jazeera in Malaysia would not change anything.
"The documentary has gone viral in Malaysia and is still shown throughout the world," he added.
Sue Al Jazeera if report false
Mahathir also urged the government to sue the media organisation if there is no truth in the documentary.
"Najib's government claims Al Jazeera is trying to subvert the government with the half-hour documentary on murder in Malaysia. It claims there is no truth in the report.
" Al Jazeera is watched by millions throughout the world. Most would believe what they see. Merely saying it is not true may convince some Malaysians but not foreigners.
"After all, during the Merdeka month, Al Jazeera showed a glowing documentary on Malaysia, including its PM. Viewers have a choice to believe which documentary.
"This new documentary would blacken not only Najib’s name but the country as well. It is not pleasant to be told the prime minister may be involved in a murder," Mahathir added.
Najib has repeatedly denied being involved in the 2006 murder case, which is often exploited by political rivals during election campaigns.
The prime minister’s close associate Razak Baginda was initially charged with abetting the murder, but was acquitted without being called to make his defence.
Two former special operations force personnel Sirul Azhar Umar and Azilah Hadri have been convicted with murdering the Mongolian national.
However, Sirul fled to Australia before the Federal Court overturned his acquittal in January. He is currently being held at an immigration detention centre in Sydney.
The Al Jazeera documentary alleged, among others, that Sirul was attempting to blackmail Najib and quoted an unnamed relative of the former policeman as claiming that Razak Baginda pulled the trigger.
Inspector-general of police Khalid Abu Bakar dismissed the allegations and announced that police are investigating Al Jazeera 's Australian-based journalist Mary Ann Jolley over her report and those who fed her wrong information.
Meanwhile, Najib claimed it was part of conspiracy to force him out of office.
