As the families of Americans celebrate the release of their loved ones held in Iran, the authorities in Tehran said they would not be freeing a businessman arrested in October and were silent on the fate of a former FBI agent who disappeared in the country. It was unclear why Siamak Namazi, 44, an Iranian American based in Dubai, was arrested in October while visiting a friend in Tehran where he had done consultant work over the previous decade. U.S. officials said Saturday that they would continue to talk with Iran to secure the release of Namazi as well as...