SEOUL, South Korea — He was one of North Korea’s deadliest secret agents. On Oct. 9, 1983, Kang Min-chul and two other North Korean agents bombed the Martyrs’ Museum in Rangoon, Burma, in a plot to kill the South Korean president, who was to have laid a wreath there. The bomb missed its mark — the president’s car had been delayed — but 17 South Koreans, including four cabinet ministers, were killed. For his deed, Mr. Kang was consigned to oblivion. North Korea denied any connection with the attack. In South Korea, where the bombing was declared a North Korean...