Police have recorded statements from 15 people regarding a statutory declaration (SD) made by former police commando Azilah Hadri.

In a statement today, Bukit Aman's Criminal Investigation Department deputy director Mohd Roze Shaari said more witnesses will be called in.

"(We want to) complete investigations before Azilah's application to review the death sentence is heard (on April 20)," he said.

In October last year, Azilah signed a sworn statement stating that he, acting on orders of then deputy prime minister Najib Abdul Razak, murdered Mongolian national Altantuya Shaariibuu in 2006.

Azilah claimed that Najib gave a "shoot to kill" order while performing a throat-slitting gesture. The policeman was also instructed to blow up Altantuya's body.

After a lengthy trial, Azilah and co-accused Sirul Azhar Umar were sentenced to death for Altantuya's murder.

Both the officers were briefly freed when the Court of Appeal overturned their conviction. During this period, Sirul fled the country and is currently at an immigration detention centre in Australia.

The Federal Court eventually reinstated their conviction.

Following the revelation of Azilah's statutory declaration, Najib performed a religious oath to state that he did not order Altantuya's killing and asked for Allah to curse him if he were lying.