Funding terrorism: Tracking resources remains a priority
The death of Osama Bin Laden could have closed one deadly chapter in American history that began on 11 September 2001, but one issue remains as long as al-Qaeda and similar terrorist groups exist - how do they finance their activities?
In October 2001 President George W Bush signed into law the Uniting and Strengthening America by Providing Appropriate Tools Required to Intercept and Obstruct Terrorism Act - the USA Patriot Act.
The US Treasury led an international fight against the financing of terrorism and was at the forefront of an expanded Department of Homeland Security.
During the past decade, the department, which employs 216,000 people, has spent more than $424bn (£256bn).
But does the death of Bin Laden indicate the work of some of these people is now redundant?
Not according to Anna Murison of the specialist intelligence company Exclusive Analysis, who says they have to be more vigilant than ever.
"The US led a very large international effort after 9/11 to unite countries to tighten up the rules on terrorist financing," Ms Murison says.
The 9/11 attacks were largely funded through the formal banking system - wire transfers of money into the US, taking cheques and travellers' cheques physically into the US, and through debit and credit cards.
Investigations suggested the cost of the attacks in New York and Washington on 11 September 2001 amounted to $400,000 (£240,000).
There has never again been such a large attack by al-Qaeda, or any effort to move such a huge amount of funds.
"What we have seen in the past few years with the tightening up of terrorist financing regulation is that attacks have become lower budget," says Ms Murison.
"The best measure for the success of the tightening of regulations has been to look at attack patterns... the degree of sophistication involved," she says.
In the West the degree of sophistication has involved lower budgets.
"These people are using back-pack bombs instead of putting people through expensive training procedures like sending them through flight school, which is what happened in the 9/11 attacks.
"The cargo aircraft plot which took place in October 2010 cost only $4,200 [£2,500]," she says.
Because al-Qaeda groups remain small and act separately, it remains difficult to track where they are and from where their funding is coming.
Funding varies widely across the different al-Qaeda groups.
In Yemen and the Arabian peninsular, much of the funding comes from personal and social networks.
In 2010 a Saudi woman was arrested having raised about $500,000, probably through her network of contacts within Saudi Arabia.
That money could be taken over as cash into Yemen, whereas in North Africa, much of the funding comes from the smuggling of drugs, weapons, tobacco, cigarettes and stolen cars.
That type of money is extremely difficult to track.
Impact of Bin Laden's death
Bin Laden was born into a wealthy Saudi family involved in construction, and that was where much of his own personal wealth came from - with estimates ranging anything from $50m to $150m.
He used his personal fortune to good effect in Afghanistan to further the Jihad cause - channelling it into hospitals as well as the fighting effort.
But in May 2010 there was the reported death of Sheikh Sa'id al-Masri, al-Qaeda's third in command in Pakistan, and believed to be its chief financial officer.
Some analysts predict the combined loss of Sheikh Sa'id and Bin Laden will be painful to al-Qaeda from a financial perspective.
However, because al-Qaeda has affiliated groups around the world with different sources of funding, the impact of Bin Laden's death on those groups could be minimal.
There have been discussions as to whether the death of Bin Laden will actually promote a flurry of support for terrorist groups, but Ms Murison says that is highly improbable.
"Al-Qaeda leaders in Pakistan have been trying for a long time to repeat the success of the spectacular attacks in the UK and the US and they haven't managed to do so," she says.
"It would be wrong to suggest that the death of Bin Laden suddenly means that they rediscover this capability," she adds.
"Where we are more likely to see reprisals is in Yemen or Saudi Arabia where businesses are more vulnerable and certainly individuals are more vulnerable to things such as kidnap and execution," Ms Murison says.
She says the strategy of the US Treasury and other organisations following terrorism financing is now focusing on identifying future hot spots.
"Perhaps they are not looking so much at the old al-Qaeda in Pakistan but starting to look at new centres of Jihad," she adds.
"For example, the US is taking a great interest in drug smuggling routes from South America into western Africa which have connections with al-Qaeda in the Islamic community there."