As failures go, the Central Intelligence Agency’s inability to pick up hints of Mr. Kim’s death was comparatively minor. But as one former agency official, speaking on condition of anonymity about classified matters, pointed out: “What’s worst about our intel is our failure to penetrate deep into the existing leadership. We get defectors, but their information is often old. We get midlevel people, but they often don’t know what’s happening in the inner circle.”

The worst intelligence failure, by far, came in the middle of the Iraq war. North Korea was building a nuclear reactor in Syria, based on the design of its own reactor at Yongbyon. North Korean officials traveled regularly to the site.

Yet the United States was ignorant about it until Meir Dagan, then the head of the Mossad, Israel’s intelligence service, visited President George W. Bush’s national security adviser and dropped photographs of the reactor on his coffee table. It was destroyed by Israel in an airstrike in 2007 after the United States turned down Israeli requests to carry out the strike…

At 10 a.m. local time on Monday, even as North Korean media reported that there would be a “special announcement” at noon, South Korean officials shrugged when asked whether something was afoot. The last time Pyongyang gave advance warning of a special announcement was in 1994, when they reported the death of Mr. Kim’s father, Kim Il-sung, who also died of a heart failure. (South Korea was caught completely off guard by the elder Mr. Kim’s death, which was not disclosed for 22 hours.)