The Islamic State suicide bomber who killed at least 169 Afghan civilians and 13 United States soldiers outside Kabul airport last month was incarcerated in Afghanistan’s notorious Bagram prison for the past four years, thanks to Indian efforts, Firstpost has learnt through credible intelligence sources.

Senior Indian intelligence sources familiar with the case have told Firstpost that he was handed over to the United States' Central Intelligence Agency by the Research and Analysis Wing in September 2017. However, the jihadist walked free on 15 August along with thousands of other dangerous terrorists held in the high-security prison, taking advantage of the chaos that ensued in the aftermath of the United State's hurried exit and the Taliban's swift takeover of the entire country.

Identified as Abdul Rehman, the jihadist was a former student of an engineering college in India and hailed from Afghanistan’s Logar province. He was the son of an Afghan merchant who frequently visited India for business.

His arrest had led to the termination of a plot by the Islamic State of Khurasan Province (IS-K) -- the Islamic State’s regional wing in Afghanistan -- to stage suicide bombings in New Delhi and other cities across the region, probably on the behest of Pakistan’s Inter-Services Intelligence Directorate (ISI).

"America’s disorganised retreat from Afghanistan has led to hundreds of highly-competent and highly-committed terrorists being set free to rejoin the Islamic State, al-Qaeda and other terrorist groups," one officer who worked on the Abdul Rehman case said.

"Literally a decade’s work on counter-terrorism has been undone by the US' failure to secure key prisoners in Bagram," he said adding that the consequences of this failure will be "very far-reaching."

The Islamic State’s South Asia magazine, Sawt al-Hind (or Voice of the Indian Subcontinent) also confirmed in this weekend's edition that the suicide bomber had earlier been arrested in New Delhi, in the course of a failed suicide-bombing plot.

The said plot was first brought into the public domain by The Indian Express in 2018 and was first detected in mid-2017 by the CIA, which had picked up intelligence from communications of IS leadership in Afghanistan and their financial support networks in Dubai.

Rehman was selected to lead the plot because of his familiarity with New Delhi, which the jihadist had visited on several occasions in connections with his family business.

Rehman, the sources said, arrived in India under cover of studying at an engineering institute in Noida. After staying in the institute’s hostel for some weeks, he moved to a flat in New Delhi’s Lajpat Nagar neighbourhood. Intercepted communications allowed RAW to insert an agent posing as a jihadist in Rehman's circle, who pretended to be furthering the plot by sourcing explosive devices and recruiting personnel.

Sources said that the Delhi Police’s counter-terrorism unit, which was led by now-Deputy Commissioner of Police Pramod Kushwaha, had conducted on-ground surveillance against Rehman for several weeks before his arrest.

RAW’s agent, the sources said, persuaded Rehman that he had recruited multiple suicide attackers and sourced enough explosives to conduct the attacks. This generated a lot of chatter in the extremists' network and caused multiple communication between the Afghan jihadist and his commanders, which the CIA was able to exploit.

Instead of prosecuting Rehman in India, the sources said, a decision was taken to extradite him to Kabul on a special flight, to facilitate the CIA's investigation. In Bagram, he was questioned by the CIA and Afghanistan’s intelligence service, the National Directorate of Security. The questioning led to the elimination of multiple Islamic State leaders in United States drone strikes till 2019.

"There’s no clarity on what happened to Abdul Rehman between his escape from Bagram and the suicide attack," one intelligence official said. "It is possible he wanted revenge, or that he was persuaded by his old jihadist friends to atone for his role in the killings of his associates in this manner."

The New Delhi suicide-bombing plot, the sources said, had begun to take shape in the summer of 2016, soon after the Islamic State’s military shura, or council, picked jihad commander Aslam Faruqi to lead the organisation. A 1977-born ethnic Pashtun from Bara, in Pakistan’s Khyber-Pakhtunkhwa, Faruqi had joined the Lashkar-e-Taiba, and operated with its units alongside the Taliban from 2007 to 2014, before leaving for Syria to join the Islamic State.

According to Antonio Giuztozzi's writings, Faruqi returned to Pakistan in 2016 and was later appointed as the leader of the Islamic State in Afghanistan, as a “result of contacts with the Pakistani ISI, which hinted to IS-K the possibility of a trade-off: the appointment of a leader linked to the ISI and the cessation of attacks against Pakistani government targets, in return for access to safe havens in Pakistan."

The Islamic State’s rapprochement with the ISI was brokered by Azizullah Haqqani, the leader of an Islamic State unit that in turn had close links to Sirajuddin Haqqani, the head of a Taliban terrorist network responsible for multiple, lethal suicide attacks across Afghanistan and who is now the interior minister of the country.

Immediate command of the New Delhi suicide operation, the sources said, rested with Amir Sultan, an ethnic-Punjabi jihadist also known by the alias Huzaifa al-Bakistani. Amir Sultan was given charge of a unit within the Islamic State, which was responsible for recruiting operatives in India, particularly in Kashmir, and for motivating them to carry out attacks in the region.

Amir Sultan’s unit included several Indian nationals, among them the only citizens of the country to stage suicide attacks overseas were dentist Ijas Kallukettiya Purayil, who was killed in a bid to storm a prison in Jalalabad last year, and his fellow Kerala resident, Muhammad Muhsin.

Last month, Firstpost had revealed that Aijaz Ahanger, Amir Sultan’s father-in-law and an ethnic Kashmiri jihadist with a long record of terror activities in Kashmir, had also escaped from Bagram prison.