A Yemeni couple may have brought inside the Jolo cathedral the bombs that exploded Sunday while Mass was being held, according to Defense Sec. Delfin Lorenzana.

Lorenza made the revelation in a radio interview Thursday morning adding that pieces of remains from victims killed in the twin explosions at the Cathedral of Our Lady of Mount Carmel are still being examined.

The pieces of remains crime scene investigators found in the church may belong to other victims killed in the explosions inside and outside the cathedral, according to Lorenzana.

President Duterte on Wednesday described the attack as a suicide bombing. Lorenzana said they are also investigating the possibility that the bombs inside and outside the church were remotely detonated.

Meanwhile, Philippine National Police chief Director General Oscar Albayalde said in a separate radio interview on Thursday that the four men caught by a security camera inside the church before the explosions turned themselves in on Wednesday.