How twice-bankrupted Melbourne businessman Peter Gerard Scully filmed himself allegedly sexually abusing two kidnapped Filipino girls aged 10 and 11 and made them dig what they believed to be their own grave has shocked Philippine investigators.

Already accused of killing a teenage Filipino girl and hiding her body in a septic tank under his "horror" house and sexually abusing a one-year-old baby, new allegations have emerged in the southern Philippines of 52-year-old Scully abusing at least a dozen children for his business selling child sex-abuse videos to internet customers worldwide.

Alleged Australian sex offender Peter Gerard Scully stands behind Philippines police investigator Angelito Magno Credit:Bobby Lagsa/Inquirer Mindanao

Eleven-year-old Daisy and her 10-year-old cousin Queenie were easy targets for Scully when they were hungry and hanging around a shopping mall in the city of Cagayan de Oro on Mindanao in September last year.

Scully's 17-year live-in partner allegedly approached them and asked "Do you want to eat?" and, after a restaurant meal, they agreed to go to the Australian's rented house in the western part of the city.