The first page of Abu Bakr’s notebook contains Arabic translations of basic English words. It ends with a safety guide for handling explosives: “Be careful.” “Don’t be afraid.” “Keep the triggers away from children.”

As Islamic State tightened its grip on this Mediterranean city last year, closing schools and restricting social life, it trained hundreds of recruits, many of them foreigners, in the Arabic language, Islam and warfare to help extend its self-declared caliphate to Europe’s doorstep, according to documents recently discovered in the group’s offices here.

The notebook of the fighter who took the name Abu Bakr was reviewed by The Wall Street Journal along with some 150 other documents left behind by militants who fled or were killed or captured in battle as Libyan militias backed by U.S. airstrikes moved in recent months to reclaim the city. The Islamic State militants were under threat on Monday of being routed in the last neighborhood they still control in the coastal city, the group’s last major bastion in the Mediterranean country.

The papers offer rare insights into how the group governed and sought to win over the population and erect a satellite state in Libya.

Detailed lists of prisoners with their offenses and corresponding punishments show how the militants enforced their austere vision of Islamic rule. Tax documents show how they tried to curry favor with some residents by confiscating money and jewelry from the wealthy to distribute to the needy, while also filling their own coffers.

The paper trail also reveals the pedestrian bureaucracy behind the group’s brutal rule in Sirte, the largest city Islamic State has ever held outside Iraq and Syria.

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