Transcript for 7 people under arrest in connection to Manchester attack

from Manchester, England, tonight. Breaking news on several fronts. The raise under way after a terror attack at a concert. Tonight the bomber, what we learned and was his brother about to bomb again? Tonight, we have new images of pieces of the bomb itself and what they reveal. We begin with ABC's chief foreign correspondent Terry Moran in Manchester. Reporter: In the terrible moment the bomb went off -- Oh, my god! Reporter: -- It left behind, amid the carnage and fear, clues to how it was made, and by whom. Tonight, those crime scene photos obtained by "The New York Times" and posted on their website reveal the bomb's sophisticated design -- the possible detonator, bloodied, carried in the suspect's left hand, investigators believe, with a small circuit board soldered inside and a protruding red wire. A mangled 12-volt battery, more powerful than those seen in most suicide bombs. Nuts and screws used as deadly shrapnel. And part of the blue karrimor backpack the bomb was carried in. Investigators now concluding that this bomber was no lone wolf. I think it's very clear that this is a network that we are investigating. Reporter: This morning, police stormed a building in central Manchester, targeting a third floor apartment. Neighbors told us they thought it was being rented as an airbnb unit. And you can't know who everybody is. Reporter: While we were there -- Police have been at this location for about three hours. And all of the sudden they have tackled this man here. They're making some kind of arrest. We don't know if it's related to the attack or not, but things happened very fast here. Reporter: It turned out, a police officer had simply been trying to break up a fight and tonight, police say all the victims have been identified. Stilling the faint, last hopes of so many. Like Charlotte Campbell, who desperately sought her 15-year-old girl, Olivia, for days. Please just phone me and come home please. Reporter: Tonight, Olivia, too, among the dead. Just heartbreaking for Charlotte. Terry Moran for us tonight from Manchester police now searching for any possible accomplices they're preparing for a huge public event this weekend? They are, David. Even as the memorial here goes, the great Manchester run city games, the largest 10k run, 35,000 runners last year will go forward this weekend, authorities say, safely. Terry, our thanks to you And the bomber himself this evening, just 22 years old.

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