The investigation quite early led us to have concerns about the movement and activities of four men, three of whom came from the West Yorkshire area,” said the head of the Metropolitan Police anti-terrorist squad, Peter Clarke.
“We are trying to establish their movements in the run-up to last week’s attack and specifically to establish whether they all died in the explosions,” Clarke told reporters.
He added that it was “very likely” that one of the suspects was among those who died in one of the bombed Underground trains, near Aldgate station in east London.
Clarke said the “complex and intensive” investigation was “moving at great speed”, following raids on six premises in the industrial city of Leeds, in northern England, home to a large Muslim population of south Asian origin.
He said a man — identity and age not revealed — was arrested in West Yorkshire, the county that includes Leeds, and that he was being transferred to London for questioning.
Closer to the capital Tuesday, police sealed off a train station and parking lot in Luton, a town north of London, and carried out controlled explosions on a car with suspected links to the attacks.