Nine days after the attack there has been a shift in the official police stance, as indicated in a BBC report which starts with:
Manchester suicide attacker Salman Abedi bought most of the components used to make the bomb himself, police have said.Many of the bomber's movements and actions were "carried out alone" in the four days prior to the attack, Russ Jackson, head of the North West counter terrorism unit, said.
But police have yet to rule out whether he was part of a wider network.
Link:http://www.bbc.co.uk/news/uk-40103563

There remain eleven men in custody, five have been released and the law allows them to be kept in pre-charge custody for up to fourteen days (with reviews at a magistrates court).

Elsewhere some have speculated the IED was not a sophisticated device.