Transcript for UK raises threat level to critical after concert terror attack

from England -- Britain's prime minister has just raised the threat level to critical. That's their highest level. It comes just 4 hours after the deadly concert attack. American pop star Ariana grande had just performed. A suicide bomber targeting the most vulnerable, children, teenagers. Terrified parents, some still hoping to find their children. 22 people were killed, dozens more rushed to the hospital. Many critically injured. Tonight, we have new images here and where the bomb was detonated just after that concert ended 57bd the suspect tonight, authorities forcing their way into his home today. We believe with Terry Moran here in Manchester tonight. ??? Reporter: They came out on a school night to see their idol, thousands of teenage girls packing the arena. Pop diva Ariana grande finishes her encore in a shower of pink balloons. At 10:33 P.M., the house lights come up, and then the sound of the bomb. Oh, my god. What's going on? What just happened? Reporter: Panic. Oh, my god! Confusion, those pink balloons popping as the audience rushes for the exits. Girls clamber over railings, dropping into the crowd, desperate to escape. Carol Taylor was there with a friend and their children. There was just smoke and there were embers coming down from the roof and people were screaming and we just ran and ran and ran. Reporter: Bethany Keeling was right near the exit when the bomb went off. I saw like a flash. Like, an explosion flash. I grabbed my friend's hand and we just ran. But we looked and we could see the bodies on the floor. Reporter: Victims lying where they'd fallen. The ground streaked with blood. The killer today identified as 22-year old british-born Salman Abedi. Police believe he detonated his suicide bomb here, in an area connecting the massive arena to the nearby train station, which then descended into chaos. When the bomb went off, many parents were waiting outside to collect their kids after the show. For some of to youngsters, it was their first concert. Joe Gregory was sitting in his car, waiting to pick up his girlfriend. He sees the flash, hears the bang. And then it hits him. No! Reporter: As ambulances screeched to the scene, and people tended to the wounded, Nick Hayward plunged into the fleeing crowd, searching for his daughter Kaitlyn. I had that moment when I was working my way up the steps of, "What am I going to find?" And in the back of your mind, you're thinking the worst. Reporter: And then you saw her -- Oh, just huge relief, huge relief. Huge relief. It was almost like she had been Reporter: Relief for one father. But tonight, sorrow for so many. These images beamed around the world -- some young fans, still clutching those pink balloons. Terry is here with us in Manchester. The uk has now raised its threat level to critical. What can we see now. Up to 5,000 military troops will now be deployed at key sites and on the streets of Britain. A striking sight in a country where ordinary policemen don't carry firearms. It will free up police resources to go on the hunt for more

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