LONDON — The man who detonated explosives at a pop concert in Manchester, England, last week, killing 22 people and wounding dozens, mainly acted alone in the days leading up to the attack, the British police said late Tuesday.
The sophisticated planning and execution of the attack had initially led the British authorities to believe that the assailant, Salman Abedi, had the support of a larger terrorist cell. That, in turn, led to fears that a bomb maker and a network of people who provided support could still be at large, and even preparing further attacks.
But as detectives moved into the eighth day of their investigation, they said that their reconstruction of the movements and actions of the 22-year-old bomber in the four days before the attack showed that he had acted mostly on his own. They did not, however, rule out the possibility that others had been involved.
To date, 16 people have been arrested in connection with the attack, though five of those have been released without charges.
“We still have a number of people in custody,” Detective Chief Superintendent Russ Jackson, who leads the counterterrorism unit for the country’s northwest, said in a statement. “We will be seeking to extend the custody of some of them as we work to understand what has gone on and whether Abedi was helped.”
More than 1,000 officers have been involved in the investigation, tracking Mr. Abedi through analysis of surveillance cameras, phone records and other interactions he had with people in the days before the attack. More than 300 pieces of digital equipment have been examined as part of the investigation, the police said.
“With specialist support, we also have a good understanding of the likely component parts of the bomb and where these came from,” Chief Superintendent Jackson said. “Our inquiries show Abedi himself made most of the purchases of the core components.”
Mr. Abedi, a Manchester resident of Libyan decent, is believed to have visited Tripoli four days before the attack, and experts say that it is likely that he received training there to build the device he used for the bombing.
As the investigation continues, the American singer who was performing on the night of the attack, Ariana Grande, announced on Tuesday that she would return to Manchester to participate in a benefit concert for the victims and their families on Sunday, alongside performers including Justin Bieber, Coldplay, Katy Perry and Miley Cyrus.
“Our response to this violence must be to come closer together, to help each other, to love more, to sing louder and to live more kindly and generously than we did before,” Ms. Grande said in a statement.