A longtime political opponent of President Ferdinand Marcos, Aquino had just landed in his home country after three years of self-imposed exile in the United States when he was shot in the head while being escorted from an aircraft to a vehicle that was waiting to transport him to prison.

An official government investigation ordered by Marcos shortly after the assassination led to murder charges against 25 military personnel and one civilian, all of whom were acquitted by the Sandiganbayan (special court).

After Marcos was ousted, another government investigation under President Corazon Aquino's administration led to a retrial of 16 military personnel, all of whom were convicted and sentenced to life imprisonment by the Sandiganbayan.

In early 1978, Aquino, still in prison, founded a political party named Lakas ng Bayan (or "LABAN")[b] to run for office in the interim Batasang Pambansa elections.

[11] First Lady Imelda Marcos arranged for Aquino to undergo surgery at the Baylor University Medical Center in Dallas, Texas, and he would be released from prison on humanitarian grounds to leave with his family for San Francisco on a Philippine Airlines flight on May 8, 1980.

Aquino spent the next three years in self-exile in the U.S., wherein he worked on manuscripts for two books and delivered several lectures and speeches critical of the Marcos government across the nation.

[c][17] In July 1983, Pacifico Castro (then Deputy Foreign Minister) warned international air carriers (including JAL) not to allow Aquino to board its planes.

[19] On August 13, 1983, Aquino, following a morning worship service, went to Boston International Airport, where he would take a flight to Los Angeles[20] to attend conferences with his fellow Filipino contacts.

[24] After going through immigration via his Marcial Bonifacio passport, Aquino would be stopped by two Taiwanese airport officials, before he (together with Kashiwahara and other members of the press) boarded China Airlines Flight 811, a Boeing 767-200 (registered as B-1836) bound for Manila, and left Taiwan at 11:15 am.

[28] On August 19, 1983, then-Assemblyman Salvador Laurel informed Chief of the Philippine Constabulary Gen. Fidel V. Ramos the arrival of Aquino, requesting "all necessary security measures be undertaken to protect the Senator in view of reported plots against his life."

[42][43] During a press conference held at 5:15 pm (four hours after the assassination), Prospero Olivas (then the chief of the Philippine Constabulary Metropolitan Command) claimed that the assailant in "his twenties, dressed in blue pants and white shirt"[d] shot Aquino in the back of the head from behind with a .357 magnum revolver;[36] however, Olivas excluded from his accounts chemistry report C-83-1136, which showed that fragments extracted from Aquino were from a .38 caliber or .45 caliber pistol.

[31] Everyone from the Central Intelligence Agency, to the United Nations, to the Communist Party of the Philippines, to First Lady Imelda Marcos were accused of conspiracy.

The board was composed of former Court of Appeals Justice Corazon Agrava[29] as chair, with lawyer Luciano E. Salazar, entrepreneur Dante G. Santos, labor leader Ernesto F. Herrera, and educator Amado C. Dizon as members.

Before the Agrava Board could start its work, President Marcos claimed that the decision to eliminate Aquino was made by the general-secretary of the Philippine Communist Party, Rodolfo Salas.

The Agrava Board conducted public hearings and requested testimonies from several persons who might shed light on the crimes, including Imelda Marcos, and General Fabian Ver, Chief of Staff of the Armed Forces of the Philippines.

A post-mortem analysis disclosed that Aquino was shot in the back of the head at close range with the bullet exiting at the chin at a downward angle, which supported Quijano's testimony.

Some airside employees of the airport on duty during the assassination gave testimonies that support that of Quijano, stating that Galman was having a conversation with one soldier when gunshots rang out.

Aquino's wife, Corazon, and children Ballsy, Pinky, Viel, Noynoy, and Kris arrived from Boston the day after the assassination.

In a later interview, Aquino's eldest daughter, Ballsy (now Aquino-Cruz), recounted that they learnt of the assassination through a phone call from Kyodo News.

[71][72] Sixteen defendants were found guilty and sentenced to life imprisonment by the Sandiganbayan in 1990[73] and ordered to pay damages to the families of Aquino and Galman.

[77] The convicts filed an appeal to have their sentences reduced after 22 years, claiming that the assassination was ordered by Marcos's crony and business partner (and Corazon Aquino's estranged cousin) Danding Cojuangco.

Aquino's death transformed the Philippine opposition from a small isolated movement to a massive unified crusade, incorporating people from all walks of life.

The middle class got involved, the impoverished majority participated, and business leaders whom Marcos had irked during martial law endorsed the campaign – all with the crucial support of the military and the Catholic Church hierarchy.

The assassination showed the increasing incapacity of the Marcos regime – Ferdinand was mortally ill when the crime occurred while his cronies mismanaged the country in his absence.

The mass revolt caused by Aquino's demise attracted worldwide media attention and Marcos's American contacts, as well as the Reagan administration, began distancing themselves.

There was a global media spotlight on the Philippine crisis, and exposes on Imelda's extravagant lifestyle (most infamously, her thousands of pairs of shoes) and "mining operations", as well as Ferdinand's excesses, came into focus.

Alicia Syquia-Quirino and three of her children were murdered by Imperial Japanese troops along during the Battle of Manila in 1945, while Doña Aurora Quezon was killed along with her daughter and son-in-law in a Hukbalahap ambush in 1949.

[82] It had been apparently dumped in a secluded area of the base where it was left to rot until its purchase by Marlon Marasigan, a retired Philippine Air Force colonel in 1997.

A proposal to display the van at the Presidential Car Museum in Quezon City was deemed inappropriate by NHCP chair Rene Escalante.

[85] Under then-President Gloria Macapagal Arroyo, the observance of this holiday became moveable – to be celebrated on the "Monday nearest August 21" every year – as part of her controversial 'holiday economics' philosophy as reflected in Republic Act No.