By Michael Buchanan
An investigation by the BBC World Service into the cost of the London bombings last July has revealed that they cost no more than a few hundred pounds to carry out.
The 7 July London bombers killed 52 commuters
As soon as Scotland Yard established the identities of the four men responsible for the London bombings on 7 July, they began investigating the financing of the attacks.
Officers now believe that Mohammad Sidique Khan, who worked as a teaching assistant, was the principal backer of the attacks and that he gave money to the other men to buy some of the materials.
The attacks by four suicide bombers on three Tube trains and a bus killed 52 people and injured hundreds.
Detectives also discovered that the men had prepared for their own deaths - they paid off some of their debts and at least one bomber is understood to have written a will.
Further investigations allowed police to put a price on the cost of executing the attacks - no more than several hundred pounds.
Loretta Napoleoni, an economist and expert on terrorist financing, told Dirty Money on the BBC World Service that the figure was part of a pattern.
Police think Mohammad Sidique Khan was the main backer
"If you look at 9/11, which cost only $500,000 to execute, and then you look at all the subsequent attacks that have taken place - going from Bali to Istanbul to Madrid to London - we actually see that the cost of the attacks is decreasing exponentially."
Still, the figure now revealed for the cost of the London bombings is very low.
The Madrid bombings - another attack on the transport infrastructure of a major European city - are estimated to have cost $10,000, approximately 10 times the cost of the London bombings.
Within days of the attacks, Chancellor Gordon Brown went to Brussels for a meeting of EU finance ministers to urge them to cooperate more closely to stop the financing of terrorism.
But the fact that London was bombed for such a cheap figure - and that the money was raised legitimately - highlights the problems that the authorities have in tackling terrorist financing.
Douglas Greenburg, who studied the financing of attacks on New York and Washington as part of the 9/11 commission, told Dirty Money: "If you have someone who is working and depositing their pay cheques into the bank, and periodically withdrawing money and at night buying components for a bomb, constructing a bomb in their basement, what's the bank going to do about that?"