MANILA, Oct 22 (Reuters) Philippine police today said they were still not sure what caused an explosion at an upscale shopping mall in Manila last week that killed 11 people and wounded more than 100.
But experts said Friday's blast could not have taken place without sabotage, despite the storage of chemicals and fuel at the basement of the Glorietta mall.
''We cannot conclude yet what happened in Glorietta,'' Avelino Razon, the national police chief, told a news conference, adding investigators were ''looking for a needle in the haystack''.
Razon said several possibilities had surfaced, including a terror attack, an accidental explosion of a pipe supplying fuel to the shopping mall's generators or a methane leak from a septic tank at the building's basement.
''At this point of investigation, the Philippine National Police does not rule out any possible angle or motive for the explosion that occurred at Glorietta 2,'' Geary Barias, police chief for the capital region, told reporters.
''The processing at the blast site will continue in order to get as much evidence and information on what could have caused the explosion.'' Police said at the weekend that the explosion was caused by a bomb and that they had founded traces of RDX, a military-grade explosive, at the location.
But Barias said there was no sign of bomb components, such as timing devices, power sources, initiators, switches or containers, in the debris.
Hermogenes Gutierrez, a civil engineer who has worked on large government projects, told Reuters it was not possible for the chemicals and fuel stored in the mall's basement to explode on their own, citing stringent security and safety standards in the construction of the building.
''Diesel fuel is not a volatile material and would not explode on its own,'' Gutierrez said, adding other chemicals, including methane in a septic tank, would not explode unless something set it off.
An army intelligence officer also dismissed the possibility of an accident, saying something had to trigger the blast, and that sabotage was the cause.
Police officials said they were still validating claims made by a small Muslim group with ties to Islamic Abu Sayyaf militants that it was behind the attack on Friday.
''We are not discounting that this group may be responsible for the incident,'' Raul Castaneda, head of the police anti-terror task force, told reporters, adding however that the Rajah Solaiman Movement has been inactive for more than a year.
A man who identified himself as Sheik Omar Lavilla called a local radio station on Saturday claiming responsibility for the attack and demanding the release of Rajah Solaiman Movement leader Hilarion del Rosario Santos, also known as Ahmed Santos.
REUTERS SS RN1253