MANILA, Philippines -- Australian forensic experts have concluded that the blast which killed 11 and injured over a hundred in a mall in Makati City last month was caused by a gas explosion and not by an improvised explosive device.

In its 13-page report, a copy of which was obtained by INQUIRER.net, the Australian Forensic Police (AFP) however did not say what had led to the blast although it noted that there were several “potential sources” which included the “sewer gas/fumes which can consist of sulphur dioxide, methane, ammonia; diesel fumes.” Australian experts also said that there were no traces of bomb parts.

Aside from the Australian experts, the Federal Bureau of Investigation (FBI) also conducted its own investigation into the explosion at the Glorietta 2 last October 19.

The Australian police ruled out bombing as the cause of the blast because “there was no evidence to suggest that the explosion had been caused and/or initiated by an improvised explosive device.”

The report added that even the FBI forensic team “had not located any evidence to suggest the use of an explosive device at the crime scene.”

At the same time, the Australian police recommended the examination of maintenance records of Glorietta 2, specifically those of the basement, scene of the explosion.

The Philippine National Police refused to make public the report of Australian experts while investigations were ongoing.

The Ayala Land Incorporated, which operates the mall, had wanted to see a copy of the report so that they could comment.

The Australian police, who assisted the local task force in its own investigation, arrived October 20 and left on October 27, according to the official report.

In their seven-day investigation, the Australian experts established that “the gas explosion occurred and originated in the basement.”

This conclusion matched the results of the PNP’s initial investigation.

PNP Chief Avelino Razon and Police Director Geary Barias, National Capital Region Police Office chief, have said that their investigators were close to ruling out a bomb as the source of the explosion.

Barias said there was pressure build-up of diesel fumes and methane gas, emitted by the malfunctioning sewage pump.

Barias also said investigators have not seen any bomb component such as timing device, power source, initiator, switches and container.

And although RDX, an ingredient of bomb component C4, was found from pieces of evidence from the blast site, it was possible that this did not come from a bomb. RDX could be reportedly found in toothpastes or deodorants.

The Australian experts also said that based on their observations, the explosion occurred after a pressure build-up in the basement.

They noted that the lid of the diesel fuel tank, located at the basement, was “lifting upwards…suggesting a pressure build-up within the tank; that the damage penetrated from the inside-out, approximately 15 centimeters wide on the top section of the tank; no apparent strike marks or inward buckling to the tank; but there was insufficient damage to the tank to indicate it as being the source of the explosion.

“It is possible that the ignition source was remote from the area of greatest fuel build-up. From the detailed scene examination, physical evidence, blast damage effects, and background information provided, it appears the explosion has occurred in the basement of Glorietta 2 as a result of an explosive fuel-air mixture being initiated by unknown means,” the report also showed.

To fully determine the cause of the blast, Australian experts also advised its counterparts to: examine the floor area of basement to determine the extent of the damage; engage independent appropriate engineers/experts to examine machinery including septic pump, exhaust system, diesel tank, control panel switches and pumps; examine CCTV footage; examine maintenance records of Glorietta 2; ensure that all relevant witness statements would be collected and evaluated for significant information; examine post-mortem reports, including location of deceased, among others.

On Wednesday, authorities were also supposed to recover the submersible pump in the basement. Barias said police could not enter the basement unless it had been declared safe.

As soon as investigators have established conclusively that the explosion was an accident, charges of negligence resulting to multiple homicide and serious physical injuries are likely to be charged against the tenants and/or owner of the origin of explosion, local authorities have said.