"We need to establish a number of things: who actually committed the attack, who supported them, who financed them, who trained them, who encouraged them," Deputy Assistant Commissioner Peter Clarke told the press yesterday. "This will take many months of intensive detailed investigation."
Sources close to the investigation told many newspapers privately that police were particularly looking for an Egyptian chemist as either a suspect or witness in the case. The man, identified in the press as Magdi el-Nashar, earned a doctorate degree in biochemistry at Leeds University and is reported to have recently taught chemistry in that city in northern England.
The Egyptian Interior Ministry confirmed in a statement today that police arrested el-Nashar, 33, in Cairo late yesterday or early today. He is reported to be now under questionning by Egyptian police with British agents present.
Three of the four suspected suicide bombers are from the Leeds area. Police have confirmed the identities of two of the men as Hasib Mir Hussein, 18, and Shehzad Tanweer, 22. Both are British-born men of Pakistani descent.
The identities of the other two bombers have not been confirmed, but they are widely reported to be another Briton of Pakistani descent and a Jamaican-born Muslim convert.
Analysts say the search for the Egyptian chemist indicates the police suspect a well-organized and experienced international network such as Al-Qaeda is behind the 7 July attacks.
David Claridge, a security expert with London-based Janusian Security Risk Management, said that the attacks show a degree of preparation that is typical of Al-Qaeda operations.
“I think it’s been fairly clear from the beginning of this, from the day of the attacks, that Al-Qaeda or some broader network was likely to have been involved even if, in fact -- as many of us suspected and were proven correct -- British citizens may have been those to have actually deliver the devices and to detonate them. And that is really borne out now with information that is coming out with the involvement of the Egyptian, in particular,” Claridge said.
Metropolitan Police Commissioner Ian Blair said today that there are "connections in other countries" to the four blasts. He did not elaborate but said Britain expects to find a clear Al-Qaeda link to the bombings.
Pakistani President Pervez Musharraf has promised British Prime Minister Tony Blair that Pakistan will provide its full support and assistance to the investigations. The two confirmed suicide bombers, Hussein and Tansweer, are known to have traveled to Pakistan, reportedly to pursue religious studies.
Alex Standish, editor of "Jane's Intelligence Digest" in London, told RFE/RL that since Al-Qaeda was evicted from its base in Afghanistan in late 2001, the organization has broken down into small cells scattered worldwide. The cells fund their own operations but trade expertise.
“Typically, an Al-Qaeda cell, or an Al-Qaeda-related cell, may consist of eight or 10 individuals," Standish characterized the cells. "Now, not all of those individuals will necessarily be from the locality [the country where the cell is located]. You may have a specialist in ideology, you may have a specialist in bomb-making skills. And not all of these individuals will still be around when the actual attacks are carried out. They may well have fled the country, passed on to other cells, and it is unlikely that these people don’t have safe houses or some kind of support network which goes well beyond the borders [for example] of the United Kingdom.”
As the hunt for the suicide bombers’ accomplices turns international, it remains unclear whether the explosives used in the attack were homemade or brought in from abroad.
Police initially said they believed the explosives could be homemade devices. Later, investigators said the bombs might be made of high-grade military explosives -- something many security analysts suggested would have been acquired in Eastern Europe.
However, the picture has been complicated by reports that police have found evidence of a low-grade homemade explosive in the bathtub of one home they raided in Leeds.
European officials speaking privately to the media said the material found in the home is made of easily obtained chemicals that require a certain expertise to turn into an explosive mix.
A similar mixture is reported to have been used by British would-be suicide bomber Richard Reid, who sought to detonate a bomb in his shoe on a Paris-to-Miami flight in late 2001. Reid, an avowed Al-Qaeda supporter, is now in prison.