Transcript for The headlines, the latest on the fast moving investigation in Manchester.

British troops are patrolling key sites after the country's terror threat index was raised to critical that's the highest level. Only if he of the twenty people killed have been publicly identified. Some people are still missing his family and friends use social media to try to look for them. ABC's Molly hunter is live in Manchester with us this morning lot of what's the latest. It mind thank you just want to say. That critical level is incredibly rare here the last time that prime minister put that threat level is critical is in July 2007. And it requires so many resource as an additional soldiers at this additional police additional security for us now. All over the country they it's unlikely it will be able this day critical for that long. In July 2007 it was quickly move back at to severe not as severe as any more comforting of course. I'm now here in Manchester the investigation is broadening this morning police say they are focusing on whether or not summit at that he acted alone. At least one person has been arrested 23 year old in south Manchester but police have not that. What his relationship was to summit at Betty now we are here in Manchester. In a town center this is where the vigil took place last night it was a beautiful vigil thousands and thousands of people thousands of strangers gathering together. To unite a rag. Common messages the masses last night Fannie and it lets you can't be got this wild wing and it's not working you can see there are flowers. Behind me that pile of course will only continue to grow and I did just wants to show you. A couple of the papers this morning. Now we hear you have. The girls will never come on dining and as we talked so much about the young victims of course there were so many preteens. And teenagers and here you've got the youngest victim eight years old. And here's the Manchester evening news. Prepares for the missing and the dead and of course many pictures of the victims there. As you did mention in your answer we will find out probably more names that pistons are still so many families. Praying for their loved ones thank tennis and in. Did that sad list will come out a little bit later on today and that days to come quite a scene there in. Manchester Molly hunter there for us thank you.

This transcript has been automatically generated and may not be 100% accurate.