SEOUL, South Korea (AP) — A desolate but lovely volcano on the North Korea-China border could be the key to unraveling the sudden, mysterious death of an exiled scion of North Korean royalty. South Korea's spy agency believes that Kim Jong Nam was assassinated this week in a Malaysian airport as part of a five-year plot by North Korean leader Kim Jong Un to kill a brother he reportedly never met. Kim Il Sung saved the Korean Peninsula, according to the official Pyongyang narrative, with daring guerrilla raids against Japanese invaders from his base on the slopes of Paektu. Because the Kim brothers shared the same exalted and heroic lineage — the "blood of Mount Paektu" — the argument goes, no matter how low profile he was, Kim Jong Nam would always pose a danger. "Kim Jong Un might have thought that he had nearly completed his consolidation of power and that taking out Kim Jong Nam would be a finishing touch to eliminate a potential source of trouble," said Koh Yu-hwan, a North Korea expert at Seoul's Dongguk University. Kim Jong Un, the youngest known son of Kim Jong Il, could have feared his brother because under a traditional Confucian value system, Kim Jong Nam, the eldest son, would have been considered the direct heir to the throne.