As Britain continued to grieve on Friday after an attack earlier this week at an Ariana Grande show in Manchester, England, that killed 22 people, investigators pressed ahead with efforts to unravel the network that is believed to assisted the bomber, Salman Abedi.

The bombing, which also killed the 22-year-old assailant, was the deadliest terrorist attack in Britain since 2005. The victims included children and parents waiting to pick up young concertgoers, and the Islamic State has claimed responsibility.

The country has been on the highest state of alert since Tuesday, indicating a further attack “may be imminent,” as investigators try to determine how the bomb was assembled and what help Mr. Abedi might have had.