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.
Three men arrested over the attack were released without charge on Tuesday.
Det Ch Supt Jackson said much of the police investigation had been working through Abedi’s last movements.
Officers have examined his movements on CCTV and other interactions he had with people as well as phone calls he made.
“Our enquiries show Abedi himself made most of the purchases of the core [bomb] components and what is becoming apparent is that many of his movements and actions have been carried out alone during the four days from him landing in the country and committing this awful attack,” said Det Chief Supt Jackson.
However, it was “vital” that police make sure he is not part of a wider network and there were a “number of things” about this behaviour that were a concern, he added.
Det Ch Supt Jackson said police were keen to find out why Abedi kept going back to the Wilmslow Road area of the city and wanted to find the blue suitcase he used during those trips.
A total of 16 people have been arrested in connection with last Monday’s attack. Five have been released without charge while 11 are still in custody.
Every police force in the UK has assisted in some way since the terror attack in Manchester, according to the National Police Chiefs Council.
Twenty-eight forces, as well as the National Crime Agency, have been helping police in Manchester on their investigation and the response to the bombing.
Det Ch Supt Jackson said police have made “huge progress” in the week since the attack but it will “take considerable time before we fully understand what has happened”.
Twenty-two people were killed and many injured after the bomber carried out an attack following an Ariana Grande concert.
The singer will be joined by the likes of Coldplay, Justin Bieber, Katy Perry and Take That at a benefit concert for victims on Sunday.
Meanwhile, Liam Gallagher played his first solo gig in Manchester on Tuesday night, with the proceeds also being donated to the victims of the bombing.
He applauded as heartfelt cries of “Stand up for the 22” rang out from the crowd in reference to those killed.
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