Police officers investigating the 7 July London bombings are searching two shops and a flat in Leeds.
Officers from West Yorkshire and the Metropolitan Police are conducting the searches - in the Beeston area, close to where three of the bombers lived.
Scotland Yard said they were searching a "combined residential and business premises" they had raided on Tuesday.
Neighbours say one of the shopkeepers, who sells computers, was questioned at a police station and then released.
Shehzad Tanweer, 22, who lived with his parents in Beeston, Mohammad Sidique Khan, 30, who lived in Dewsbury, West Yorkshire, and worked in a Beeston primary school, and Germaine Lindsay, 19, detonated bombs on Tube trains.
Hasib Hussain, 18, who lived in the Leeds district of Holbeck, blew up the number 30 bus at Tavistock Square.
Lindsay lived in Aylesbury, Buckinghamshire, but he also had connections with Beeston.
The attacks claimed a total of 52 lives.