Police say it is "vital" that they make sure Salman Abedi was "not part of a wider network"
Three men arrested in connection with the Manchester terror attack have been released without charge.
The men - aged 20, 24 and 37 - were among 16 people arrested by police. 11 now remain in custody.
More than 1,000 officers are working on the investigation to piece together what happened and whether others had worked with 22-year-old bomber Salman Abedi.
The suicide attack at Manchester Arena killed 22 people and injured dozens of others.
Detective chief superintendent Russ Jackson said the release of potential suspects "can be expected in investigations of this nature as we corroborate accounts that have been provided."
In a statement, he added: "There has been huge progress made over the week and the speed of the inquiry remains the same. It will be a long investigation and it will take considerable time before we fully understand what has happened."
Police say they believe many of the actions and movements of Abedi in the days leading up the attack were "carried out alone".
Mr Jackson added: "It is vital that we make sure that he is not part of a wider network and we cannot rule this out yet. There remain a number of things that concern us about his behaviour prior to the attack and those of his associates which we need to get to the bottom off."
Latest update pic.twitter.com/BkDopt0XvE— G M Police (@gmpolice) May 30, 2017