A defaced Islamic State flag is emblazoned on a wall in Tikrit, Iraq, in 2015. ISIS will generally claim responsibility for an attack within one day, though it can sometimes take longer.
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A police officer stands on duty outside a residential property in Fallowfield, in southern Manchester, on Wednesday as investigations continue into the bombing at the Manchester Arena.
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A sign with flowers and candles lay on the ground after a vigil in Albert Square in Manchester, England, on Tuesday, the day after a bombing at an Ariana Grande concert killed at least 22 victims.
Balloons and flowers filled a memorial in Albert Square in central Manchester, in northwest England, in tribute to the victims of the Monday night attack at the Manchester Arena.
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