This is an excellent article at the NYT.
EXCERPT
BAMAKO, Mali — The cash filled three suitcases: 5 million euros.
The German official charged with delivering this cargo arrived here aboard a nearly empty military plane and was whisked away to a secret meeting with the president of Mali, who had offered Europe a face-saving solution to a vexing problem.
Officially, Germany had budgeted the money as humanitarian aid for the poor, landlocked nation of Mali.
In truth, all sides understood that the cash was bound for an obscure group of Islamic extremists who were holding 32 European hostages, according to six senior diplomats directly involved in the exchange.
The suitcases were loaded onto pickup trucks and driven hundreds of miles north into the Sahara, where the bearded fighters, who would soon become an official arm of Al Qaeda, counted the money on a blanket thrown on the sand. The 2003 episode was a learning experience for both sides. Eleven years later, the handoff in Bamako has become a well-rehearsed ritual, one of dozens of such transactions repeated all over the world.
While European governments deny paying ransoms, an investigation by The New York Times found that Al Qaeda and its direct affiliates have taken in at least $125 million in revenue from kidnappings since 2008, of which $66 million was paid just last year.
In news releases and statements, the United States Treasury Department has cited ransom amounts that, taken together, put the total at around $165 million over the same period.
These payments were made almost exclusively by European governments, who funneled the money through a network of proxies, sometimes masking it as development aid, according to interviews conducted for this article with former hostages, negotiators, diplomats and government officials in 10 countries in Europe, Africa and the Middle East. The inner workings of the kidnapping business were also revealed in thousands of pages of internal Qaeda documents found by this reporter while on assignment for The Associated Press in northern Mali last year.