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, British police said late Tuesday.

The sophisticated planning and execution of the attack initially led 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 second week 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 have been released without charges.

More than 1,000 officers have been involved in the investigation, tracking 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, police said.

Abedi, a Manchester resident of Libyan descent, 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.

New York Times