The financing arrangements for the September 11 attacks on the US appear to have gone unnoticed by security agencies except on one occasion.
When Mohamed Atta, thought to be the leader of the 19 hijackers, opened a bank account in southern Florida in June 2000, a wire transfer of $69,985 from the Gulf three months later prompted SunTrust Bank to make a suspicious transaction report to the US Treasury's Financial Crimes Enforcement Network.
Like most of the 125,000 similar reports sent in each year, it went unremarked, until it was discovered by investigators searching for information on the people behind the hijacking of the four airplanes.
The rest of the $500,000 or so needed to finance the attacks arrived in the US through much smaller transfers or in cash or travellers cheques for amounts that rang no alarm bells with the banks.
Financial investigators and regulators have been striving since September 11 to improve their systems for spotting terrorist funds and interrupting their flow around the world.
Evidence uncovered by the Financial Times suggests it has been relatively easy for al-Qaeda to move its money through the global banking system. But the organisation has used other channels that are less easy to block.
In 1993 Jamal Ahmed al-Fadl, bin Laden's finance officer during the 1991-96 period when al-Qaeda was based in Sudan, was sent from Sudan to Amman in Jordan with money for the Abu Ali group, a militant Islamist group and part of the al-Qaeda network in Jordan and the Palestinian territories.
Al-Fadl flew to Amman with $100,000 in $100 bills in a suitcase also containing clothes, and was escorted through customs by Abu Akram, his contact in Jordan.
"He talked with one of the customs people and they didn't check my bag," al-Fadl said earlier this year when giving evidence in the trial in New York that convicted four men of the bombings of the US embassies in Kenya and Tanzania in 1998.
That money had been drawn out of a Khartoum bank, al-Shamal Islamic Bank, one of several used by al-Qaeda in Sudan. Al-Shamal was founded in 1984 with authorised capital of $20m and started banking operations in 1990, said the bank's acting general manager, Ismail Mohamed Osman.
A US State Department report in 1996 and a French investigation into the bank separately concur that bin Laden invested $50m in the bank on his arrival in Sudan in 1991, an allegation Mr Ismail denies.
Mr Ismail said al-Qaeda opened accounts in Sudanese pounds and US dollars with the bank for two of its companies, but that was the limit of the bank's relationship with bin Laden.
"Bin Laden contacted us as a businessman, and opened a foreign currency account in the name of the al-Hijra company [Al-Hijra Construction, which built roads for the Sudanese government]," Mr Ismail said. "He never came himself to the bank. The foreign account was replenished from outside Sudan, mainly from Gulf states and from America, through bank transfers. Over three or four years, probably one million dollars went through these accounts."
Bank records show that when Sudan was forced - under intense Saudi and US pressure to ask bin Laden to leave in 1996 - the accounts at al-Shamal held 554,000 Sudanese pounds and a mere $99.58. This money, according to Mr Ismail, is still there.
Al-Qaeda has been able to move money around the world through al-Shamal's correspondent network of banks that co-operate with the Sudanese bank in cross-border transactions. Al-Shamal's correspondents have included France's Credit Lyonnais, Germany's Commerzbank, Standard Bank of South Africa and Saudi Hollandi bank in Jeddah in which ABN Amro of the Netherlands has a 40 per cent stake.
These external links were used in 1993 when al-Qaeda bought an aircraft in the US to move Stinger ground-to-air missiles from Peshawar in Pakistan to Khartoum.
The money was wired from the Wadi al-Aqiq account at al-Shamal bank via Bank of New York to a Bank of America account held in Dallas, Texas by Essam al-Ridi. Al-Ridi, an Egyptian flight instructor who met bin Laden in Pakistan in 1985, flew the plane to Khartoum.
In view of the scale of bin Laden's investment in Sudan - about $30m - and the relatively small amounts held at al-Shamal and other banks in Khartoum, it is clear that a large part of al-Qaeda's financial arrangements did not involve banks at all.
When al-Qaeda was planning the 1998 bombing of the US embassies in Kenya and Tanzania, it turned to an older method of transferring funds. It used the hawala system, which allows money to be submitted to an office in one country and handed over for payment elsewhere, without the cash actually travelling. The two offices simply confirm receipt and payment.
Take the case of Mohamed al-Owhali. Four days after he was supposed to have died as a suicide bomber in Nairobi, al-Owhali received $1,000 at the Nairobi office of Dihab Shill, a Somali- based hawala money transfer company.
Al-Owhali had no money and his identity papers had been destroyed in advance of his intended death. But he was able to receive funds because the al-Qaeda contact who had sent cash from Yemen had written a note on the transfer which, according to Ismail Jama Ali, the manager of the Dihab Shill office, said: "This person doesn't have any proper documents ... please give him without documents." The money was duly handed over.
Many of the payments made through these informal systems pass through Dubai, in the United Arab Emirates. Dubai is an entrepot for the region and has no exchange controls, though the authorities are now seeking to improve oversight of the banking system.
US investigators from the US Treasury's Financial Crimes Enforcement Network this month ordered the freezing of all accounts connected with another Somali-owned hawala, al-Barakat, which has its headquarters in Dubai, and the UAE authorities were quick to respond.
On November 7, Paul O'Neill, the US Treasury secretary, accused al-Barakat, along with a Swiss-based financial management company, al-Taqwa, of "raising, managing, investing and distributing funds" for al-Qaeda. Treasury officials said that not only was the al-Barakat network used to transmit funds for al-Qaeda, it also shared profits of "tens of millions of dollars" with it each year.
Suspicion of Barakat first emerged in 1999. An alert banker at BankBoston, now part of FleetBoston, was combing through computer data on money transfers at the bank as part of a routine check for money-laundering activities. He noticed many wire transfers into Barakat's account were just below $10,000 - the amount that requires companies to file a report with federal authorities.
BankBoston ordered the account closed. But the Barakat operation, run out of Dorchester, Massachusetts, and Ottawa in Canada, had no trouble finding another place to park its money. Barakat's managers simply switched their accounts to Massachusetts' Citizens Bank and the Key Bank in Portland, Maine.
In an interview with the FT, Ahmed Nur Jumale, chairman of Barakat, denied any link with bin Laden or al-Qaeda and said the US had fallen into a trap laid by business and political rivals of his company.
Francois Seznec, a former Gulf-based banker who lectures in Arabic politics and finance at Georgetown university in Washington DC, believes much of al-Qaeda's liquid funds will be held in such centres. "If you want to look for terrorist funds, you will have to look in the banks and money-changers of Dubai," he said.
US investigators believe about half the $500,000 that the hijackers spent on the September 11 plot was sent by Mustafa Ahmad, who is today regarded by investigators as bin Laden's finance chief, via Dubai money exchanges through Citibank in New York and on to Florida.
Such money transfers have given investigators their most solid link to bin Laden's al-Qaeda network. That they were all but undetectable until the terrorist attack reflects the skill with which al-Qaeda used international financial networks.
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