Execution prompts surprise, fear inside North Korea
Many North Koreans living here in the South are using covert contacts to get information about what is happening back home.
Their reports suggest a rise in the number of indoctrination sessions across the country, with people being required to write letters pledging their loyalty to the regime and also letters of "self-reflection" examining their own behaviour.
The sudden execution of the country's second-most senior statesman, North Korean groups here say, has created a considerable amount of "surprise, bafflement" and "fear".
Jang Jin-sung left North Korea in 2004 and now runs a news website devoted to reporting events inside the country.
"You can really feel a sense of crisis when you hear people's voices on the phone" Jang Jin-sung said.
"They seem to really suffer from fear: it resonates in their voices. They say times have changed now that the leader himself is getting directly involved in removing his family members."
The fear inside North Korea may have grown, but there is also a suggestion from some sources that the execution has diminished Kim Jong-un's authority.
One trader told a contact here in Seoul that "half the public in North Korea believes Chang Song-thaek was a scapegoat - purged to take the blame for the country's economic failures".
He also said that, away from the public indoctrination sessions, North Koreans were discreetly talking amongst themselves, asking how Kim Jong-un could do this to his uncle?
A report from another trader seemed to confirm this, saying that the execution showed Kim Jong-un's lack of morality and that attitudes towards him had "turned in a negative direction".
"The deification of the North Korean leader has completely changed with the purge of Chang Song-thaek," Jang Jin-sung said. "There is no longer a god-like aura around the country's leader."
North Korea has been keen to project a sense of stability following the execution. Kim Jong-un has continued his regular public appearances - visiting various military and commercial projects.
And state media has been trumpeting its achievements over the past year - new roads, health-care centres and ski-resorts.
But South Korea's government is unconvinced by the mask of stability. President Park Geun-hye warned before meeting high-level defence officials on Monday that the execution had left the Korean Peninsula in a "grave and unpredictable" situation.
It was uncertain which political direction North Korea would move in, she told government officials, and "reckless provocations" by Pyongyang could not be ruled out.
Military action by North Korea over the coming days could signal disruption within the country, and a need to pull its people together.
Kim Jong-il (d)×
Kim Jong-il was one of the most secretive leaders in the world.Tales from dissidents and past aides created an image of an irrational, power-hungry man who allowed his people to starve while he enjoyed dancing girls and cognac.
But a different picture was painted by Sung Hae-rim, the sister of one of his former partners in her memoir, The Wisteria House.
She describes a devoted father and a sensitive, charismatic individual, although she admits even those closest to him were fearful of him.
North Korean media depicted him as a national hero, whose birth to the country's founder, Kim Il-sung, was marked by a double rainbow and a bright star.
The youngest sister of the late Kim Jong-il and the wife of the man formerly regarded as the second most powerful figure in North Korea, Chang Song-thaek.
She has held a wide range of important Workers' Party positions including being a member of the all-powerful Central Committee.
Her promotion to four-star general made Kim Kyung-hee the first North Korean woman ever to achieve such status.
Analysts say Kim Kyung-hee and her husband were seen as mentors for the new leader Kim Jong-un when he came to power in 2011. But news of her husband's execution in December 2013 suggests the most significant upheaval in North Korea's leadership since Mr Kim succeeded his father.
Chang Song-thaek (d)×
Chang Song-thaek was married to Kim Kyung-hee, the younger sister of the late Kim Jong-il. When the inexperienced Kim Jong-un became the new leader in 2011, the couple were widely thought to be acting as his mentors.
In December 2013, the powerful uncle - who sat on the country's top military body - was denounced by the state-run news agency for corruption. Images were shown of him being removed from a Politburo meeting by uniformed guards. He was then executed.
Mr Chang's execution is the biggest upheaval in North Korea's leadership since Mr Kim succeeded his father.
Kim Jong-nam, 39, is Kim Jong-il's eldest son.
Sung Hae-rang, the sister of Kim Jong-nam's deceased mother Sung Hae-rim, has written in her memoir that Kim Jong-il was extremely fond of Kim Jong-nam and was pained to be away from him. Like his half-brothers, Kim Jong-nam studied at an international school in Switzerland.
His chances of succession appeared to be ruined when, in 2001, Japanese officials caught him trying to sneak into Japan using a false passport. He told officials that he was planning to visit Tokyo Disneyland.
Some analysts argued that he may have been forgiven by his father, as there is precedent for the regime reinstating disgraced figures after a period of atonement. Confucian tradition also favours the oldest son.
But in a rare interview while on a trip to China last year, Kim Jong-nam said he had "no interest" in succeeding his father.
Kim Sul-song, 36, is Kim Jong-il's daughter born to his first wife, Kim Young-sook.
Reports say she has worked in the country's propaganda department, with responsibility for literary affairs.
One South Korean report said she had also served as her father's secretary.
Kim Jong-chul, 29, studied at an international school in Switzerland. He works in the WKP propaganda department.
His mother, Ko Yong-hui, is said to have been the North Korean leader's favourite consort.
However, Kenji Fujimoto, the pseudonym of a Japanese sushi chef who spent 13 years cooking for Kim Jong-il, has written that the leader considered his second son "no good because he is like a little girl".
Kim Jong-un, the second son of Kim Jong-il and his late wife Ko Yong-hui, was anointed "the great successor" by Pyongyang.
Like his older brothers, he is thought to have been educated abroad.
A Japanese sushi chef who worked for Kim Jong-il for 13 years up to 2001 said that he "resembled his father in every way, including his physical frame".
Speculation that he was being groomed to succeed his father had been rife for years.
Since taking power, he has presided over a long-range missile test, North Korea's third nuclear test and most recently the execution of his uncle, Chang Song-thaek.
Ri Sol-ju was introduced as Kim Jong-un's wife in state media reports about the opening of an amusement park in July 2012.
Reports simply said he attended the event with his wife, "Comrade Ri Sol-ju".
Little more is known about Ri Sol-Ju, although there has been much speculation about her background since pictures first emerged of Kim Jong-un with an unidentified woman. There is a North Korean singer of the same name, but she is not now thought to be the same person.
State media did not mention when the couple got married.
The grandson of Kim Jong-il and nephew of leader Kim Jong-un has said he wants to "make things better" for the people of his country.
Kim Han-sol, 17, spoke of his dreams of reunification of the two Koreas in an television interview in Bosnia, where he is studying. Kim Han-sol said he had never met his grandfather or uncle.
He described an isolated childhood spent mostly in Macau and China, after his birth in Pyongyang in 1995. In the future, he said he pictured himself going to university and then ''volunteering somewhere''.