How could it happen? That is the question authorities in the US are desperately seeking to answer amid an ongoing operation to recover bodies after the collapse of a bridge in Minneapolis. At least four people are known to have died but eight are still missing and the death toll is expected to rise. Minnesota Senator Amy Klobuchar expressed the shock of the nation: “A bridge in America shouldn’t just fall down and that’s why we have called for this investigation. I’m very pleased the National Transportation Safety Board Chair is already there.” Divers are trying to locate bodies thought to be trapped in ten vehicles in the Mississippi river. But in the fast-flowing, murky waters the operation is difficult and dangerous. There is concern now across the country about the state of similar bridges. Federal Transport authorities have called on all states to inspect some 700 bridges of a similar construction.