On Wednesday bomb sniffer dogs uncovered explosive material on a truck at the southwestern Ringhals plant during a routine security check by personnel. The material was then sent by helicopter to a laboratory which determined it was explosive, though the material lacked a detonating device . Police are investigating possible sabotage but have not identified any suspects. "We don't know what the idea behind this was, what was the plan and what may have failed. These are some of the questions we will try to answer with our investigation," police spokesman Ingmar Nilja told The Wall Street Journal. According to the Swedish Radiation Safety Authority all security has been raised at the country's three nuclear power plants, up one notch from the lowest level.