Four Americans and their pilot were all killed when a small aircraft crashed into the roof of a shopping mall in Melbourne, Australia on Tuesday morning, local time. The propeller plane had taken off from a nearby airport and reported an engine failure, officials said. It exploded as it struck the building near the end of the runway, about an hour before the mall was scheduled to open. The plane had been headed for King Island, a popular tourist destination. No one else was harmed in the incident.