Police have searched an address in Cambridge as part of the investigation into failed car bomb attacks in Glasgow and London.
The Metropolitan Police confirmed the search had taken place but would not reveal the exact address.
Eight people have so far been arrested in connection with the attacks - all with links to the NHS.
It has emerged that four of the suspects were in Cambridge in 2005 and that they knew each other.
Dr Kafeel Ahmed and Dr Bilal Abdullah, both arrested at Glasgow airport after a burning car was driven into doors of main terminal, were "best mates", their associate in Cambridge Shiraz Maher has told the BBC.
Dr Abdullah was a resident in the city in 2001 and again in 2005.
On Thursday, Hicham Kwieder, secretary of the Cambridge Muslim Welfare Society, said he knew Dr Abdullah and last saw him about a year ago.
He said: "I talked to him, like many other people. He was a nice person. I knew him as someone who attended our mosque.
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"I met him after the invasion [of Iraq]. He felt pain that the country was divided and people were fighting each other.
"I recognised his photograph in the paper. I was shocked. Whatever information we have will be passed on to the police. We're helping police with their inquiries."
Dr Abdullah rented a room in a house owned by the mosque in Cambridge in 2001, he added.
A spokesman for the society told the BBC that they invited police into the mosque, but the premises were not searched.
Instead representatives of the mosque went to Parkside police station and spoke to officers there for more than seven hours.
Dr Ahmed is believed to have been a research student in the science and technology department at Anglia Ruskin University.
A spokeswoman for Anglia Ruskin University said: "We are aware of media speculation about possible links between recent events at Glasgow Airport and one of our research students.
"We are co-operating fully with the police in their inquiries. At this time identities are still unclear and it would therefore be inappropriate to comment further."
Dr Ahmed's brother Sabeel - arrested near Liverpool Lime Street station after the attacks - was also a frequent visitor to the city, the BBC has learnt.
And Dr Mohammed Asha, arrested along with his wife, Dana, on the M6 near Sandbach, Cheshire, had a two month placement at Addenbrooke's Hospital in the city.
Sabeel Ahmed and Dr Abdullah are also known to have been close friends while in Cambridge.
A friend said that Dr Abdullah and Sabeel Ahmed were close: "Sabeel and Bilal were like clowns, loud and funny and cracking jokes all the time. Sabeel used to pay flying visits to the city."
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