A former intelligence officer for Saddam Hussein was the mastermind behind ISIL’s takeover of northern Syria, according to a report by Der Spiegel that is based on documents uncovered by the German magazine.

Der Spiegel, in a long story published over the weekend called “Secret files reveal the structure of Islamic State,” said it gained access to 31 pages of handwritten charts, lists and schedules that amount to a blueprint for the establishment of a caliphate in Syria, which the Islamic State in Iraq and the Levant (ISIL) has declared it has set up.

The documents were the work of a man identified by the magazine as Samir Abd Muhammad al-Khlifawi, an Iraqi national and a former colonel in the intelligence service of the late Iraqi dictator's air defense force. Khlifawi went by the pseudonym Haji Bakr.

Der Spiegel said the files suggest that the takeover of northern Syria was part of a meticulous plan overseen by Khlifawi using techniques — including surveillance, espionage, murder and kidnapping — honed in Saddam's security apparatus.

Khlifawi was reportedly killed in a firefight with Syrian rebels in January 2014, but not before he had helped ISIL secure swaths of Syria, which in turn strengthened ISIL’s position in neighboring Iraq.

“What Bakr put on paper, page by page, with carefully outlined boxes for individual responsibilities, was nothing less than a blueprint for a takeover,” the story by Der Spiegel reporter Christoph Reuter said.

“It was not a manifesto of faith, but a technically precise plan for an ‘Islamic Intelligence State’ — a caliphate run by an organization that resembled East Germany's notorious Stasi domestic intelligence agency.”

The story describes Khlifawi as being “bitter and unemployed” after U.S. authorities in Iraq disbanded the army by decree in 2003. From 2006 to 2008 he was reportedly in U.S. detention facilities, including Abu Ghraib prison.

In 2010, Khlifawi and a small group of former Iraqi intelligence officers made the devout Abu Bakr al-Baghdadi the official leader of ISIL, with the goal of giving the group a “religious face,” the story says.

Two years later, the magazine says, Khlifawi traveled to northern Syria to oversee his takeover plan, choosing to launch it with a collection of foreigners including novice fighters from Saudi Arabia, Tunisia and Europe alongside battle-tested Chechens and Uzbeks.

Iraqi journalist Hisham al-Hashimi, whose cousin was in ISIL with Khlifawi, describes the former officer as a nationalist rather than someone whose main motivation was religious. The story argues that the secret to ISIL’s success lies in its combination of opposites — the fanatical beliefs of one part and the strategic calculations of another, led by Khlifawi.

Der Spiegel said it obtained the papers after lengthy negotiations with rebels in the Syrian city of Aleppo who seized them when ISIL was forced to abandon its headquarters there in early 2014.

The Soufan Group, a risk consultancy that closely monitors ISIL, said in an assessment of the group in June that it was Khlifawi who nominated Baghdadi, the current leader of ISIL, as the caliph of the organization.

With the instrumental help of Khlifawi, the foundations for ISIL as an organization with effective management abilities were laid. In a report last fall on the group’s structure, the Bloomberg news agency said in the group’s operation was “more akin to General Motors that to a religious dynasty.”

Al Jazeera and Reuters