The ‘secret among secrets’: Where is Kim Jong-un?

Speculation about the North Korean leader’s health has been swirling since he missed the country’s biggest annual celebration: the April 15 birthday of his grandfather, Kim Il-sung, who founded the Stalinist state.

Kim Jong-un’s last public appearance was more than two weeks ago, on April 11, when he presided over a Politburo meeting. This is not the first time Mr. Kim has disappeared from public view for weeks at a stretch, but rumors have exploded. One report in the American news media said he was “in grave danger” after surgery. Others speculated that he was dead.

Spy satellites have in recent days spotted a train “probably belonging” to Mr. Kim in Wonsan, an east coast town where Mr. Kim’s family has a seaside compound. And a South Korean news report said on Saturday that the U.S. had detected preparations for a missile test in Sondeok, farther up the east coast, where North Korea has launched missiles in the leader’s presence.

A defector’s view: Joo Sung-ha, a North Korean who fled the country and is now a journalist in the South, said on Facebook that it was reasonable to believe that Mr. Kim had health problems. But, Mr. Joo said, he had zero trust in news reports detailing whether and why the North Korean leader faced a grave medical emergency.

Information about the health of the Kim family is “the secret among secrets” in the North, Mr. Joo said.

Watch: Our video team spoke with experts about how they track Mr. Kim’s whereabouts.