Former premier Dr Mahathir Mohamad raised questions about Altantuya Shariibuu's murder because he was unaware of details on the police investigations into the matter, said inspector-general of police Khalid Abu Bakar.

Speaking to reporters at KLIA2 today, Khalid said this includes allegations made by fugitive police commando Sirul Azhar Umar.

"Of course (Mahathir) doesn't know what actions we have taken (and) what investigations we have conducted.

"What Sirul recently raised has also been probed by us and we are of the view that there is nothing (in his claim) for us to continue (with) the investigation," said Khalid.

Khalid said this when asked to comment on Mahathir's blog post yesterday, where he claimed that there was no investigations on Sirul's claims that he was "following orders".

"This is a human life. It would be very cruel for Sirul to die for just following orders," Mahathir had said.

Sirul and Azilah Hadri, both members of Prime Minister Najib Abdul Razak's security detail when Altantuya was murdered in 2006, had their conviction upheld in January and sentenced to death.

However, Sirul managed to flee the country before the final appeal.

In fact, the police chief said Sirul had many opportunities to raise the claim but he did not.

"My response to Yang Amat Berbahagia Tun Mahathir: this case happened eight years ago.

"Sirul has plenty of opportunities to raise this issue - before the trial, during the police investigation, after the trial, while waiting for the appeal - but why now? This is the big question," he asked.

Nevertheless, the police has probed everything Sirul has raised and found "there is nothing much to be done", he added.

"What we know now, we knew it before," he said.