The convoy of cars bearing the black al-Qaeda flag came at high speed, and the manager of the modest grocery store thought he was about to get robbed. Mohamed Djitteye rushed to lock his till and cowered behind the counter. He was dumbfounded when instead, the al-Qaeda commander gently opened the grocery's glass door and asked for a pot of mustard. Then he asked for a receipt.

Confused and scared, Djitteye did not understand. So the jihadist repeated his request. Could he please have a receipt for the USD 1.60 purchase?

This transaction in northern Mali shows what might seem an unusual preoccupation for a terror group: al-Qaeda is obsessed with documenting the most minute expenses.

In more than 100 receipts left in a building occupied by al-Qaeda in the Islamic Maghreb in Timbuktu earlier this year, the extremists assiduously tracked their cash flow, recording purchases as small as a single light bulb.

The often tiny amounts are carefully written out in pencil and coloured pen on scraps of paper and Post-it notes: The equivalent of USD 1.80 for a bar of soap; USD 8 for a packet of macaroni; USD 14 for a tube of super glue.

The accounting system on display in the documents found by The Associated Press is a mirror image of what researchers have discovered in other parts of the world where al-Qaeda operates, including Afghanistan, Somalia and Iraq.

The terror group's documents around the world also include corporate workshop schedules, salary spreadsheets, philanthropy budgets, job applications, public relations advice and letters from the equivalent of a human resources division.

Taken together, the evidence suggests that far from being a fly-by-night, fragmented terror organisation, al-Qaeda is attempting to behave like a multinational corporation, with what amounts to a company-wide financial policy across its different chapters.

"They have to have bookkeeping techniques because of the nature of the business they are in," said Brookings Institution fellow William McCants, a former adviser to the US State Department's Office of the Coordinator for Counter-terrorism.

"They have so few ways to keep control of their operatives, to rein them in and make them do what they are supposed to do. They have to run it like a business."