Police have detained 14 people after last Monday's suicide bomb attack at Manchester Arena that left 22 dead.
Salman Abedi detonated a bomb at the end of a concert by US singer Ariana Grande.
MI5, the British Military Intelligence, has launched a "post incident investigation" into how Abedi was overlooked, despite warnings that he might be a threat.
In total 16 people were arrested but a woman and a 16-year-old boy were later released.
Adam Gilchrest has more on this and other stories.
Now increasingly it looks like he was absolutely a part of a network with other accomplices.— Adam Gilchrist, UK correspondent
A thousand police officers are working on this investigation.— Adam Gilchrist, UK correspondent
MI5 is already looking at whether they missed stuff, whether effectively there was a net through which Salman Abedi slipped. It has already been suggested at least three times he was reported for extremest behavior and extremest expression of his thoughts.— Adam Gilchrist, UK correspondent
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