Part of the answer can be found in more than 15,000 pages of internal Islamic State documents I recovered during five trips to Iraq over more than a year.

The documents were pulled from the drawers of the desks behind which the militants once sat, from the shelves of their police stations, from the floors of their courts, from the lockers of their training camps and from the homes of their emirs, including this record detailing the jailing of a 14-year-old boy for goofing around during prayer.

https://nyti.ms/2HcrFcn
https://nyti.ms/2HcrFcn+