On the 22nd of May 2017, Salman Abedi walked across the foyer of the Manchester Arena towards an exit door with a bulging rucksack.
As thousands left the concert hall, many to greet parents there to collect them, at 10.31pm he detonated his shrapnel-laden device.
Could he have been spotted and challenged before then?
The answer, according to the chairman of the inquiry into the attack, is that he could have been – numerous times.