In the days and weeks that followed, the army, socio-political, and religious groups blamed the coup attempt on the Communist Party of Indonesia (PKI).

Under the New Order and to this day, the movement is usually referred to as the Thirtieth of September Movement/PKI (Indonesian: Gerakan 30 September/PKI or "G30S/PKI") by those wanting to associate it with the PKI, and this term is also sometimes used by the current government.

While the Central Intelligence Agency (CIA) initially believed that Sukarno orchestrated all of it,[13] several outside sources found inconsistencies and holes in the army claims, notably Benedict Anderson and Ruth McVey who wrote the Cornell Paper that challenged it.

[17] In need of Indonesian allies in its Cold War against the Soviet Union, the United States cultivated a number of ties with officers of the military through exchanges and arms deals.

[18] At around 3:15 am on 1 October, seven detachments of troops in trucks and buses dispatched by Lieutenant Colonel Untung Syamsuri (commander of Tjakrabirawa, the presidential guard), comprising troops from the Tjakrabirawa Regiment (Presidential Guards), the Diponegoro (Central Java), and Brawijaya (East Java) Divisions, left the movement's base at Halim Perdanakusumah Air Force Base, just south of Jakarta to kidnap seven generals, all members of the Army General Staff.

Meanwhile, their main target, Coordinating Minister of Defense and Security and Armed Forces Chief of Staff, General Abdul Haris Nasution managed to escape the kidnap attempt by jumping over a wall into the Iraqi embassy garden.

They did not occupy the east side of the square – the location of the armed forces strategic reserve (KOSTRAD) headquarters, commanded at the time by Major General Suharto.

They proclaimed that this was to forestall a coup attempt by a 'Generals' Council' aided by the Central Intelligence Agency, intent on removing Sukarno on Armed Forces Day, 5 October.

Sukarno traveled to Halim 'after learning that there were troops near the Palace on the north side of Lapangan Merdeka' and also claimed (later) 'that this was so he could be near an aircraft should he need to leave Jakarta'.

Further radio announcements from RRI later that day listed 45 members of the G30S Movement and stated that all army ranks above Lieutenant Colonel would be abolished.

At 5.30 am, Suharto, commander of the Army's Strategic Reserve (KOSTRAD), was woken up by his neighbor[29] and told of the disappearances of the generals and the shootings at their homes.

[30][31] Most of the rebel troops fled, and after a minor battle in the early hours of 2 October, the Army regained control of Halim, Aidit flew to Yogyakarta and Dani to Madiun before the soldiers arrived.

[32] Following the 7 am radio broadcast on RRI, troops from the Diponegoro Division in Central Java took control of five of the seven battalions and other units in the name of the 30 September movement.

With the support of the Army, and fueled by horrific tales of the alleged torture and mutilation of the generals at Lubang Buaya, anti-PKI demonstrations and then violence soon broke out.

This Indonesian exile literature was full of hatred for the new government and written simply, for general consumption, but necessarily published internationally.

School textbooks followed the official government line[44] that the PKI, worried about Sukarno's health and concerned about their position should he die, acted to seize power and establish a communist state.

According to later pronouncements by the army, the PKI manipulated gullible left-wing officers such as Untung through a mysterious "special bureau" that reported only to the party secretary, Aidit.

Robert Cribb states that "the Movement aimed to throw the army high command off balance, discredit the generals as apparent enemies of Sukarno, and shift Indonesian politics to the left so that the PKI could come to power rapidly, though probably not immediately"; Cribb believes that the PKI acted because it feared that, given Sukarno's failing health, the system of Guided Democracy would soon collapse, allowing the right-wing faction in Indonesian society to take over the country.

[49] John Roosa writes that the 30 September Movement was an attempt to purge the Indonesian government of anti-communist influences, that failed because it was "a tangled, incoherent mess".

They claimed that the action was a result of dissatisfaction on the part of junior officers, who found it extremely difficult to obtain promotions and resented the generals' corrupt and decadent lifestyles.

Dale Scott draws attention to the fact the side of Lapangan Merdeka on which KOSTRAD was situated was not occupied, and that only those generals who might have prevented Suharto seizing power (except Nasution) were kidnapped.

[6] He also alleges that the fact that the generals were killed near an air force base where PKI members had been trained allowed him to shift the blame away from the Army.

[52] Scott also implicates the CIA in the destabilization of the Indonesian economy in 1965,[51] and notes that investment by US corporations in Indonesia increased in the months prior to the movement, which he argues indicates US foreknowledge of the plot.

It mentions the military's cooperation with Washington after the latter's failure in taking over Sumatra, an area which at that time contained strong support for Marxism and therefore constituted a threat for the Western bloc, particularly the US.

The role of the Foreign Office and MI6 intelligence service of United Kingdom, then Indonesia's colonial neighbor on the island of Borneo, has also come to light, in a series of exposés by Paul Lashmar and James Oliver in The Independent newspaper in December 1998,[56][57] as well as their book, Britain's Secret Propaganda War.

To weaken the regime, the Foreign Office's Information Research Department (IRD) coordinated psychological operations in concert with the British military, to spread black propaganda casting the Communist Party of Indonesia (PKI), Chinese Indonesians, and Sukarno in a bad light.

[60] In October 2021, further light was shed on the United Kingdom's role when declassified documents revealed that the government had covertly deployed black propaganda in order to urge prominent Indonesians to "cut out [the] communist cancer".

In his testimony intended for the PKI leadership, he assesses the strengths and weaknesses of the 30 September Movement, particularly those of its presumed leader, Kamaruzaman Sjam.

Likewise, the highly publicized story about the movement's female participants; torturing and castrating the seven captured officers in Lubang Buaya turned out to be a fabrication, presumably by psychological warfare specialists.

Furthermore, the two forces did not have efficient means of communication between them; the movement itself shut down the city's telephone system when it took over the telecommunications building, and neither group had walkie-talkies or other radio devices to relay plans back and forth.