"My personal theory is that the incident was perpetrated by simple criminal groups extorting from the bus company," he said.
Rafanan said Scene of the Crime Operations (SOCO) investigators recovered from the site fragments of a grenade which exploded in a box as it was being lifted from the last row of seats by bus conductor Louie Melanio.
Initial reports said the blast was so powerful Melanio was killed and bus driver Angelito Espej suffered head injuries.
However, Rafanan said the bus driver and a helper who was cleaning the middle section of the bus were not injured.
The grenade was not contained in a stereo component, but in a box marked for stereo components, and that no timing device was found among the debris, he added.
Sources who asked not to be named said the police in Central Luzon have been asked by higher authorities to downplay the incident so as not to cause fear among foreign delegates to the Association of Southeast Asian Nations summit slated in Cebu City this month.
"I don’t think it was the handiwork of (Jemaah Islamiyah) terrorists who would otherwise have used a more powerful bomb rather than just a grenade," the source said.
Rafanan said the box that contained the grenade was left in the back portion of the bus at the Victory Liner terminal in Barangay Bajac-Bajac in Olongapo.
"A terrorist would have put it somewhere in the middle," he said.
Rafanan said the passengers had already disembarked when the conductor found the box in the last row of seats.
"I would even discount the possibility that the New People’s Army (NPA) was responsible for it," he said. — Ding Cervantes