Faisal Shahzad paid for his botched Times Square bomb attempt with cash: $1,300 for a Nissan Pathfinder, a Kel-Tec rifle that goes for $400, airplane tickets overseas and lesser sums for firecrackers, propane and gasoline.
Federal agents want to know where he got the money.
Investigators believe the three men detained Thursday following raids on Long Island and elsewhere in the Northeast provided money to Shahzad, but it was not known whether they were aware the cash was paying for an act of terrorism, Attorney General Eric Holder said Thursday.
Matthew Levitt, a former intelligence official at the U.S. Treasury and now a senior fellow at The Washington Institute for Near East Policy, said it's quite possible for those involved in a courier network of the kind authorities appear to be investigating to not know where the money they handle ends up, or for what purpose it's ultimately used.
Foreign-born residents of the United States routinely deliver dollars to their countries of birth, and also bring cash back with them, Levitt said. These courier networks, built on bonds of family or friendship, are, for the most part, completely benign, he said.
But after press exposure in 2006 of how investigators track terrorism dollars through the formal financial system, terrorism financiers have sought new ways to move money, and courier networks have become more popular, Levitt said.
"The use of cash couriers for illicit purposes, for terrorism, is on the rise, in part because terrorists don't want to put all their eggs in one basket," said Levitt, who has testified before Congress on terrorism financing.
The courier network Levitt describes is one of several remittance systems used by traditional cultures to move money across borders. These systems can sometimes be used by people wishing to hide income, by drug dealers and, most recently, terrorists, said Edward Rodriguez, another former Treasury official, who supervised investigations into illegal money transfers.
Drug dealers involved in such systems are easier to catch, because they have to move huge amounts of cash, Rodriguez said. But terrorists' movement of money "is the worst" because the amounts are relatively small - thousands of dollars at a time, versus millions and tens of millions in drug money, he said.
Moving small amounts of money "will ring less bells," Rodriguez said.
Mike Balboni, the state's former deputy secretary for public safety and homeland security adviser, said terrorists abroad have begun a new effort to bring the kind of smaller, less expensive bomb strikes they use overseas to American soil.
The small-bomb approach is cheap because it doesn't involve high-tech weaponry or particularly sophisticated planning, Balboni said. Courier networks are perfect for meeting the funding needs of such operations, he said, and have an added advantage: cash transactions are anonymous.
By following the money, Balboni said, investigators will learn more about the players in Shahzad's support apparatus, but he cautioned that in these circumstances, linking cash to a specific crime can be difficult.