Magdy El-Nashar, who studied at North Carolina State University in the United States and the University of Leeds in northern England, came to Egypt from London on vacation and had intended to go back to Britain to continue his studies.
But in a strange twist, Egypt's Interior Minister was quoted as saying on Saturday that the 33-year-old el-Nashar had no links to al-Qaida.
Habib el-Adli told al-Gomhuria newspaper that Western and Arab media had drawn hasty conclusions about El-Nashar.
The Egyptian Interior ministry said "El-Nashar denied having any relation with the latest events in London". "He pointed out (to questioners) that all his belongings remained in his apartment in Britain."
A security official said Britain was pressuring Egypt to hand el-Nashar over, but Egypt was trying to determine if there was evidence against him that would warrant doing so.
If Egypt does hand him over, it may ask in return for Britain to extradite militant suspects Egypt has been seeking, the official said, speaking on condition of anonymity for security reasons.
In Leeds, authorities searched el-Nashar's town house in a complex of two-story brown brick apartments. The home was surrounded by blue and white police tape and covered in scaffolding draped in white plastic sheeting. Forensic teams in white coveralls were carting out material.
Police raided el-Nashar's house
in the town of Leeds
Detectives searching the apartment found signs that quantities of a compound called TATP, or triacetone triperoxide, had been converted into a powerful explosive, The Times newspaper reported.
TATP is a highly unstable explosive made from commercially available chemicals.
Leeds shop raided
Also on Friday, police in Leeds raided a shop selling Islamic books and DVDs just blocks from where at least two of the four bombers lived, and they seized materials.
Muslim leaders have said the young bombers might have been inspired by radical literature. It was not immediately clear whether any of the four bombers had links to the shop, but neighbours speculated that the owner or manager may have met the suspects at a nearby youth centre.
Three of the bombers who carried out last week's terror strikes were Britons of Pakistani origin. Pakistani intelligence officials said on Friday that local authorities were looking into a connection between one of the three Britons and two al-Qaida-linked groups in that country.
Police also raided a shop in
Leeds that sold Islamic books
"What we expect to find at some stage is that there is a clear al-Qaida link, a clear al-Qaida approach, because the four men who are dead, who we believe are the bombers, are in the category of foot soldiers," police Commissioner Sir Ian Blair told BBC radio.
British and FBI officials investigating the possible al-Qaida connection in the London attacks were also looking into the Egyptian-born biochemist el-Nashar.
ABC News, citing unidentified officials, reported that the attacks were connected to an al-Qaida plot two years ago in Lahore, Pakistan.
Names on a computer that authorities seized last year from Muhammad Naeem Noor Khan, an alleged Pakistani computer expert for al-Qaida, matched a suspected cell of young Britons of Pakistani origin, most of whom lived near Luton, where the alleged bombers met up on their way to London shortly before last week's blasts, according to the report.
Authorities have now discovered ties between 30-year-old Mohammed Sidique Khan - one of the London bombers - and members of that cell who were arrested last year, ABC said.
"What we expect to find at some stage is that there is a clear al-Qaida link"
Sir Ian Blair,
UK police commissioner
FBI agents in Raleigh, North Carolina, had been involved in the search for el-Nashar, 33, who had been a graduate student there.
One of the bombers identified by police as Hasid Hussain,18, allegedly set off the 7 July bomb that killed 14 people aboard a central London bus. That blast occurred nearly an hour after three London underground trains blew up, and investigators don't yet know what Hussain did during that hour or when he boarded the bus.
Trying to map out Hussain's movements, police appealed for information from anyone who might have seen him in or around King's Cross station, where the four suspects parted ways.
They released a closed-circuit television image showing him wearing a large camping-style backpack as he strode through a train station in Luton, outside London, about 2½ hours before he allegedly blew up the No. 30 bus.
He had a mustache and wore jeans, a white shirt, and a dark zip-up top or jacket.
Police officially identified two of the bombers on Thursday - Hussain and Tanweer, who they say attacked a subway train between Liverpool Street and Aldgate stations.
Both were Britons of Pakistani ancestry, as was Khan.
Reports say the fourth attacker was Jamaican-born Briton Lindsey Germaine.