Former prime minister Dr Mahathir Mohamad today revealed that convicted murderer Sirul Azhar Umar had also served as his own bodyguard before.

However, Mahathir said when Sirul worked for him, the Special Action Unit commando had not ended up murdering anyone.

"The man who is said to have done it (murder) was one of my bodyguards. Sirul was looking after me at that time.

"He didn't murder anyone at that time. It couldn't have been me (who ordered the killing)," he told a dialogue organised by What Youth Should Know (WYSG).

Mahathir was referring to Sirul's claim that he had been instructed to kill Mongolian national Altantuya Shaariibuu.

The former premier in a blog posting on Thursday targeted Prime Minister Najib Abdul Razak for not addressing Sirul's claims other than to dismiss it as "utter rubbish".

Sirul served as bodyguard to Najib, then deputy prime minister, when the murder took place in 2006.

Altantuya was murdered purportedly after demanding a cut of commission payments from a submarine deal during the period when Najib was the defense minister.

Najib has denied ever meeting Altantuya.

'Not fair for Sirul to hang'

Today's function was Mahathir's first public appearance after his stinging blog post on Sirul's claim for a revisit of the murder investigation. 

Students present at the dialogue wasted no time in raising about the Altantuya murder case immediately after the floor was open for questions.

Addressing this, Mahathir said it was a very "serious thing" to accuse someone of murder and he did not know who wanted Altantuya dead.

Nonetheless, he said Sirul had admitted that he was instructed to carry out the hit but the person instructing the hit has never been revealed.

"You can't go and hang a person when he was just doing his duty.

"He has been trained to take orders and carry out orders, and when he does what he is trained to do, (and) you want to hang him (for it), that is not fair.

"It is not just and not fair, and we cannot tolerate this kind of thing," said Mahathir.

The event today was titled: "Vision 2020: Mistakes Made, Lessons Learnt and Ways to Move Forward" which is part of the WYSK global leadership series.