Executive Secretary Eduardo Ermita said law enforcement authorities were ordered to strengthen their inter-agency coordination and intelligence gathering to identify the bombers as early as two weeks ago.
"There seems to be a pattern," Ermita said. "First, they do it in the morning and, second, (the bomb attacks are) not meant to hurt. Really, they are just meant to call attention."
He said law enforcers will continue their investigation into the bombings and will not stop until the perpetrators are identified and brought to justice: "We should end all these unscrupulous activities."
Press Secretary Ignacio Bunye said the government is confident that the Philippine National Police (PNP) will unmask and "bring to justice these agents of fear and terror" in due time.
Bunye also allayed fears that the bomb attacks would push President Arroyo to declare another state of emergency, as she did in February to quell a reported conspiracy to oust her.
"I believe there is no basis for these worries," he said. "Let us just await the results of the investigation."
An explosion damaged a police truck parked at the National Capital Region Police Office (NCRPO) headquarters at Camp Bagong Diwa in Taguig City.
It was the second blast to hit a police vehicle and the fourth explosion in the past week.
A previously unknown group calling itself the Taong Bayan at Kawal (Citizens and Soldiers or TABAK) claimed responsibility for the bombings, NCRPO chief Director Vidal Querol said.
He said the spate of bombings in Metro Manila was meant to embarrass and taunt the PNP, but he refused to confirm reports that TABAK was indeed responsible for the bombings.
The group first got attention last week after claiming responsibility for the bombing of the Grepalife building along Sen. Gil Puyat Avenue in Makati City and the weekend bombings of police stations in the City of Manila and Quezon City.
The group denied any involvement, however, in a pre-dawn market grenade blast in Lipa City that wounded eight people Sunday.
Also on Sunday, a bomb that investigators believe was homemade exploded in a bus being used as a mobile police station in Quezon City, blowing a hole in the vehicle’s side but causing no injuries.
PNP chief Director General Arturo Lomibao ordered an immediate investigation into the attack and reiterated an earlier appeal for the public to remain calm and vigilant.
PNP spokesman Senior Superintendent Samuel Pagdilao Jr. said investigators are still working to establish whether the same group was responsible for all four blasts — including the Grepalife building blast and a bomb attack on the gatehouse of Lubao, Pampanga town Mayor Dennis Pineda, son of suspected jueteng lord Rodolfo "Bong" Pineda. The Grepalife building houses the offices of Pacific Plans, which is facing lawsuits from the beneficiaries of its educational plans.
The PNP is now tailing individuals linked to TABAK, PNP Directorate for Investigation and Detective Management (DIDM) chief Director Marcelo Ele Jr. said, adding that the group’s ultimate objective is destabilization through discrediting the government and the PNP as an institution.
"The bombs were not intended to kill or injure or cause intensive damage to property. But it certainly aims to sow fear and anxiety. It is the objective of destabilizers and, apparently, they wanted to (make a) crack within our ranks," Ele said.
He said the series of blasts "is a matter that the police are concerned with."
"We are discounting the possibility that some persons (involved in the attacks) are linked with the PNP and AFP (Armed Forces of the Philippines)," he added.
Ele’s statement contrasted with an earlier statement made by Pagdilao that "police are taking the statement of TABAK with prudent suspicion that some quarters may just be riding on these incidents to promote their own agenda... As far as we are concerned, it (TABAK) is non-existent."
Ele said his office is currently monitoring some personalities behind the TABAK group but refused to elaborate pending further investigation.
This developed as the PNP Bomb Data Center (PBDC) reported that trinitrotoluene (TNT) and cyclotrimethylenetrineitramine (RDX), both highly volatile explosives, were used as the main components in the bombs detonated in Metro Manila and Pampanga.
Bomb analysts said fragments and debris recovered from the explosion sites showed traces of TNT from the scene of an explosion aboard a police bus in Diliman, Quezon City and the junked van in Camp Bagong Diwa.
The PNP said chemical analysis at the bombed gate of the house of Mayor Pineda also indicated the use of RDX.
Traces of TNT were also found in the Batangas and Lipa City explosions, but police considered neither incident to be connected to the bombing incidents in Metro Manila and Pampanga.
Investigators are reconstructing the improvised bombs so they can determine the make of the devices and the "signature" of the bombers to establish a profile of suspects or identify any known group that may have perpetrated the attacks.
The small amount of explosives used indicates that the attacks are definitely not the handiwork of known terrorist groups like the Jemaah Islamiyah, Abu Sayyaf, or even the New People’s Army (NPA), Ele said.
He also asked the public not to panic, but to remain vigilant and immediately report any suspicious-looking individuals and packages to the Bomb Data Center for proper management of suspected explosives. The Bomb Data Center can be reached at phone numbers 412-0062; 412-0063 and 412-0065.