[Alvin Walton]

From what I read the blast took place outside of the security zone but was in the building.
My local arena for example has a large foyer area with concessions, ticket sales and an assembly area that is a public area. You dont need tickets at this point so you dont go thru any security. I assume that it was similar to Manchester.
Its going to get to the point where will will have to rope off the whole city block to stop these kind of bombings.