The purge also could spread and bring down more people, Cha said. "When you take out Jang, you're not taking out just one person — you're taking out scores if not hundreds of other people in the system. It's got to have some ripple effect."
South Korean intelligence officials say two of Jang's closest aides were executed last month.
Narushige Michishita, a security expert at the National Graduate Institute for Policy Studies in Tokyo, suggested that Jang's removal shows "that Kim Jong Un has the guts to hold onto power, and this might have shown his will to power, his willingness to get rid of anything that stands in his way."
One of the biggest opportunities for the world to see what might happen next will come Dec. 17, the second anniversary of Kim Jong Il's death. North Korea watchers will be closely following whether Jang's wife, Kim Kyong Hui, the younger sister of Kim Jong Il, and other figures are present in official ceremonies marking the day.
Jang's removal leaves no clear No. 2 under Kim, whose inner circle now includes Vice Marshal Choe Ryong Hae, Premier Pak Pong Ju and the ceremonial head of state, Kim Yong Nam.
News of Jang's execution was trumpeted across the nation by North Korea's state media — with unusually vitriolic outbursts on TV, radio and in the main newspaper — as a triumph of Kim Jong Un and the ruling party over a traitor "worse than a dog" who was bent on overthrowing the government.
Pyongyang residents crowded around newspapers posted at the capital's main subway station to read the story. State media said Jang was tried for treason by a special military tribunal and executed Thursday.
"He's like an enemy who dares to be crazy enough to take over power from our party and our leader," said Pak Chang Gil, echoing the media's official line. "He got what he deserved."