By Agence France-Presse
Altantuya Shaariibuu was shot dead and her body blown up with military-grade plastic explosives near Kuala Lumpur.
The murder was the most shocking aspect in a scandal involving allegations that an associate of recently toppled Prime Minister Najib Razak arranged huge kickbacks for the purchase of French submarines in 2002.
The case captivated Malaysia for years and there have long been allegations that Najib -- defence minister at the time of the deal -- and his wife Rosmah Mansor were involved. They have steadfastly denied the claims.
Two government bodyguards were convicted of the killing and sentenced to death. One subsequently fled to Australia, where he is in detention, and maintains he was ordered by "important people" to carry out the murder.
Altantuya's father visited Malaysia this week. He met new Prime Minister Mahathir Mohamad, who backed re-opening the investigation, and lodged a fresh police report about the murder.
"I can confirm we are reopening investigations," national police chief Mohamad Fuzi Harun was cited as saying by The Star newspaper.
"We will conduct our duties without fear or favour."
Eric Paulsen, head of local rights group Lawyers for Liberty, told AFP that Najib should be among the new witnesses to be interviewed by the police.
"We want to know why Altantuya was killed and who ordered her killing," he said.
Malaysians broke the six-decade stranglehold on power of Najib's coalition at elections last month, and voted in a reformist alliance headed by 92-year-old Mahathir.
Altantuya was the mistress of Najib's associate, Abdul Razak Baginda, and was alleged to have demanded a cut in the submarine deal for translating during negotiations.
Abdul Razak was cleared in 2008 of abetting the murder.
The bodyguard who fled to Australia, Sirul Azhar Umar, recently said he is willing to assist any new government investigation into the case, a potential major breakthrough.