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.