More executions are anticipated as the purge continues. Unconfirmed reports from Seoul suggest that Kim might be going after another of his mentors: Ri Su Yong, who was appointed ambassador to Switzerland in 1988 and served as Kim's guardian while the boy was attending school in Bern.
Outside experts are concerned about the implications far beyond the North Korean power structure.
"If Kim Jong Un is capable of this, if there is no direct capacity for restraint, what are the implications?" said Scott Snyder, a Korea expert with the U.S.-based Council on Foreign Relations.
"Watching what happened with Jang makes you think of the nightmare scenarios," he said.
The most frightening nightmare would be the young, impetuous leader misusing North Korea's crude nuclear arsenal. North Korea has conducted three nuclear tests and has at least intermediate-range missile capability.
In March, for no discernible reason, Pyongyang declared itself to be in a "state of war" with South Korea and threatened the United States with "thermonuclear war." The tantrums prompted a rare public chastisement from Chinese leader Xi Jinping.
"We are concerned. There are a lot of questions here, including the safety of North Korea's nuclear weapons,'" said Zhang Lianggui, a North Korea expert at the Communist Party's Central Party School in Beijing.
A more pedestrian worry is who will be running things now. Jang oversaw most of North Korea's trade, maintaining the balance between various military-run companies that sell coal, iron ore and seafood in China and in turn import most of the country's consumer goods.
"In running North Korea Inc., he was very effective at making money for the regime. The question now is who is going to replace him," said John Park of Harvard University's John F. Kennedy School of Government.
China stands to be most directly affected by the turmoil in North Korea. Among the many accusations leveled against Jang were selling North Korean natural resources such as coal and iron ore to Chinese mining companies at prices that were too low, and improperly leasing a port to China in the Rason special economic zone on the Sea of Japan.
Moreover, Beijing is likely to be in a difficult position diplomatically if Jang's underlings, many of whom work in China, attempt to defect to avoid being swept up in the purge.
"Seeing Jang's execution, anybody connected to him has a sense of what will happen if they return, so it is very likely there will be people who seek asylum," said Sohn Kwang-joo, editor of the Daily NK, a Seoul-based news service that focuses on North Korea.
Analysts believe, however, that most North Koreans who are not directly swept up in the purge will fall in line behind Kim Jong Un.
Kim Young-soon, a 77-year-old former dancer from Pyongyang who now lives in Seoul, likens Kim to the young rulers of the ancient Korean dynasties.
"Kim Jong Un is young, but so were other heirs of the throne in the ancient kingdoms," Kim said. "Even if an heir is only 10 years old, one still has to uphold the leader.
"That's what the three generations of Kim dynastic rule are all about."
Times staff writer Demick reported from Beijing and special correspondent Choi from Seoul.