Documents Of ISIS Leaked

Looks like tens of thousands of ISIS documents have been leaked. Where did they come from? We don't know:

Documents listing the names of Islamic State fighters have been touted around the Middle East for months, dangled in front of media outlets for large sums of money.
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Ramsay said he met the source of the documents in Turkey, an individual calling himself Abu Hamed who had been in the Free Syrian Army rebel group and switched to Isis before becoming disillusioned with it.
Sky said the documents were on a memory stick stolen from the head of Isis's internal security police.
The Syrian opposition news website, Zaman al-Wasl, in a report billed as "exclusive" and published before Sky's, said it had the personal data on 1,736 fighters and that its documents had come from Isis's general administration of borders.