Sirul Azhar Umar, the convicted murderer of Altantuya Shaaribuu, has written a personal letter to Prime Minister Dr Mahathir Mohamad reiterating his willingness to spill the beans on the matter.

According to former Umno leader Khairuddin Abu Hassan, Sirul handed him the letter when he met Sirul at the Villawood Detention Camp in Sydney today.

"We spoke for about one-and-a-half hours, and Sirul looked healthy and calm in the detention camp. Insya-Allah, I am very confident that the truth behind Altantuya's murder will soon be revealed.

"During the meeting, Sirul handed me a letter to be given to the prime minister which I do not know the contents of. The letter was placed in a sealed envelope and I will pass it to the prime minister when I come back home in the next few days," said Khairuddin in a statement.

According to Khairuddin, Sirul also said that he missed his family back home.

"Sirul looks extremely energetic now and is no longer in fear as he believes in a new judicial system in Malaysia under Pakatan Harapan."

In an interview with Malaysiakini last month, Sirul had said that he was willing to tell all on Altantuya's murder provided he was given a full pardon on his return to Malaysia.

Sirul has been in detention at the Australian Immigration and Border Protection Department's facility in Sydney for the past three years.

He had fled to Australia before the Federal Court upheld the death sentence on him and chief inspector Azilah Hadri guilty for Altantuya's murder.

The Court of Appeal overturned their sentences in 2013 but upon the prosecution’s appeal, they were upheld by the Federal Court.

Azilah is on death row in Kajang Prison. He has also applied for a pardon.

Altantuya was murdered on a secluded hilltop in Puncak Alam between 10 pm on Oct 19, 2006, and 1.30am the following day.