The Liberal Party's campaign rally was held to proclaim the candidacies of eight Senatorial bids as well as the candidate for the Mayoralty race in Manila. As a crowd of about 4,000 gathered to hear speeches, two hand grenades were reportedly tossed on stage.
Casualties
Among those killed instantly were a 5-year-old child and The Manila Times photographer Ben Roxas. Almost everyone on stage was injured, including incumbent congressman for Palawan and future senator Ramon V. Mitra Jr., incumbent Senator Jovito Salonga, Senator Eddie Ilarde, Senator Eva Estrada-Kalaw, Liberal Party president Gerardo Roxas, Sergio Osmeña, Jr., son of former President of the Commonwealth of the Philippines Sergio Osmeña, Atty. Martin B. Isidro who served as Councilor, Vice Mayor and Congressman for the City of Manila, Ambrosio "King" Lorenzo, Jr. who served as the 2nd District Councilor of Manila, and Ramon Bagatsing, the party's mayoral candidate for the City of Manila. Salonga was among those most seriously injured. The blast left him blind in one eye and deaf in one ear. Small pieces of shrapnel remained lodged in his body until his death in 2016. Councilor Ambrosio "King" Lorenzo, Jr. was in a coma for two weeks. He lost sight in his left eye and hearing on the same side. Ramon Bagatsing, the Liberal Party mayoralty candidate for Manila, lost his left leg and suffered a crushed right cheek bone and a shattered right arm.
Suspects
Suspicion of responsibility for the blast initially fell upon incumbent President Ferdinand Marcos, whom the Liberals blamed for the bombing; however, in later years, some prominent personalities associated with the event have laid the blame on the Communist Party of the Philippines under José María Sison. The matter has never been resolved. Jovito Salonga, in his autobiography, states his belief that Sison and the CPP were responsible. Former New People's Army commander, retired Armed Forces of the Philippines Brig. General Victor Corpus has also made statements alleging that Sison ordered the bombing of the political rally. Corpus wrote in the autobiographical prologue to his 1989 book Silent War that he was present when some leaders of the CPP discussed the bombing after it took place. In a 2004 interview with journalist Max Soliven, Corpus affirmed that Sison dispatched the cadre who attacked the meeting with a hand-grenade. Based on interviews of The Washington Post with unnamed former Communist Party of the Philippines Officials, it was alleged that "the party leadership planned -- and three operatives carried out -- the attack in an attempt to provoke government repression and push the country to the brink of revolution... Sison had calculated that Marcos could be provoked into cracking down on his opponents, thereby driving thousands of political activists into the underground, the former party officials said. Recruits were urgently needed, they said, to make use of a large influx of weapons and financial aid that China had already agreed to provide." José María Sison continues to deny these claims, and the CPP has never released any official confirmation of their culpability in the incident. Marcos blamed the communists and so responded by suspending the privilege of the writ of habeas corpus. Most historians continue to suspect Marcos to have perpetrated the bombing as a pretext for his declaration of martial law. There were a series of deadly bombings in 1971, and the CIA privately stated that Marcos was responsible for at least one of them. The agency was also almost certain that none of the bombings were perpetrated by Communists. US intelligence documents declassified in the 1990s contained further evidence implicating Marcos. A proven false flag attack took place with the attempted assassination of Defense MinisterJuan Ponce Enrile in 1972. President Nixon then approved Marcos' martial law move on the rationale that the country was being terrorized by Communists.
As a response to the incident, Marcos issued Proclamation No. 889, through which he assumed emergency powers and suspended the writ of habeas corpus - an act which would later be seen as a prelude to the declaration of Martial Law more than a year later.
Radicalization of the moderate opposition
Historians note that Marcos' suspension of the writ of Habeas Corpus was the event that forced many members of the moderate opposition, including figures like Edgar Jopson, to join the ranks of the radicals. In the aftermath of the bombing, Marcos lumped all of the opposition together and referred to them as communists, and many former moderates fled to the mountain encampments of the radical opposition to avoid being arrested by Marcos' forces. Those who became disenchanted with the excesses of the Marcos administration and wanted to join the opposition after 1971 often joined the ranks of the radicals, simply because they represented the only group vocally offering opposition to the Marcos government.
Bearing on the election
In a setback for Marcos' ruling Nacionalista Party, the Liberals took six of the eight contested Senate seats, as well as the Manila mayoralty with then Congressman Ramon Bagatsing defeating the incumbent Antonio Villegas for the mayorship of the country's premiere city.
Commemoration
On August 21, 2002, President Gloria Macapagal-Arroyo unveiled a commemorative marker in Plaza Miranda in honor of the nine innocent civilians killed in the blast.
