Liezyl Margallo, 23, led police to a house in 2015 where they discovered the body of a 12 year-old girl who Scullly allegedly held as a sex and torture slave for months before strangling her and burying her body in a shallow grave.

She is expected to testify in court against 52 year-old Scully in the most shocking cases of child abuse and trafficking that Philippine officials have seen.

Police allowed Margallo, a former prostitute, to go free at the time of Scully's arrest in a part-Australian Federal Police operation in 2015 because they had not gathered evidence against her.

But they have been hunting her for more than 12 months after evidence emerged that she was the masked and naked woman shown in a video called Daisy's Destruction which Scully is alleged to have sold to clients across the world for $10,000.

The video shows an 18-month old baby girl  tied by her feet upside down while being sexually assaulted.

Welfare workers say the girl remains deeply traumatised and becomes hysterical when memories of her abuse are triggered.

Scully, a former Melbourne businessman who fled Australia in 2011 to escape fraud charges, has pleaded not guilty to 75 charges in a court in the city of Cagayan de Oro, forcing at least 10 of his alleged victims to go through the ordeal of testifying, despite repeatedly telling Philippine media he was "remorseful" for what he had done to children.

Eight of the children aged up to 12 are in the custody of the Department of Social Welfare.

The girl that Scully allegedly murdered was a former city scavenger who Margallo allegedly recruited with promises of food and schooling.

Two other girls were allegedly forced to dig their own graves before escaping.

Appearing in court last September wearing a prison T-shirt and runners, Scully refused to comment to Fairfax Media but laughed and joked with other prisoners.

Jaime Umpa, the chief prosecutor in the case, has called for the death penalty to be re-introduced so that Scully could be executed.

Philippine president Rodrigo Duterte, a former provincial mayor known as "The Punisher" is pushing for lawmakers to reintroduce the death penalty, including for rape and murder.

Margallo was arrested last week walking along a beachfront with two British men on Malapascua island near Cebu.

She initially claimed she was someone else but admitted her identity after being shown copies of arrest warrants and her photograph.

Margallo will face charges that include human trafficking and child abuse for which she could receive multiple life sentences if convicted.

"If I were describe her (Margallo) I would call her a savage girl for what she has done to the kids. I think that description fits her," a lead investigator Dominador Cimafranca told reporters.

Scully's trial is expected to take years in Philippine's log-jammed judicial system.

He has told guards at the jail where he is being held that he was sexually abused by priest when he was child growing up in Victoria.