One of the two men being held by police over the murder of soldier Drummer Lee Rigby has been discharged from hospital and moved into custody in a south London police station, the Scotland Yard said.
Michael Adebowale, 22, was arrested on suspicion of the attempted murder of a police officer.
The move comes six days after Adebowale and Michael Adebolajo, 28 had attacked the soldier in Woolwich, south-east London, and hacked him to death.
Both the accused were shot and injured by police at the scene near Woolwich Barracks on Wednesday.
They have been under police guard in hospital.
Adebowale will be interviewed by detectives from the Metropolitan Counter Terrorism Command.
Police will have 24 hours to question him before they have to apply for an extension. After a total of 96 hours, they must decide whether to charge him or release him.
The Metropolitan Police earlier said that the men would not be questioned until they had been discharged from hospital, and the time they had spent under arrest so far would not count towards the maximum amount of time they could legally be held without charge.
Both men are British of Nigerian descent.
Of the eight other people arrested in connection with the attack so far, five have been bailed and two released without charge.
Police are continuing to hold a 50-year-old man on suspicion of conspiracy to commit murder.
Meanwhile, the family of the second murder suspect, Michael Adebolajo, have expressed "horror" at the killing.
"As a family, we wish to share with others our horror at the senseless killing of Lee Rigby and express our profound shame and distress that this has brought our family," they said in a statement.
"We wish to state openly that we believe that there is no place for violence in the name of religion or politics.”
"We believe that all right thinking members of society share this view, wherever they were born and whatever their religion and political beliefs.”
"We wholeheartedly condemn all those who engage in acts of terror and fully reject any suggestion by them that religion or politics can justify this kind of violence," the statement added.