MANILA, Philippines -- Australian investigators in Manila say they have found no sign a bomb caused the giant hole in a Qantas jumbo jet's fuselage that forced a harrowing emergency landing in the Philippines.

Neville Blyth, senior investigator of the Australian Transport and Safety Bureau, said the focus is on an oxygen bottle missing from the cargo hold. The hold was left exposed when a section of the 747-400's metal skin ripped away 29,000 feet over the South China Sea on Friday.

Blyth told a news conference Sunday that tests for bomb residue were negative and that Philippine officials had bomb-sniffing dogs go through the hold, finding no indication of explosives.