If Kim Jong-nam was assassinated, it was likely the result of direct orders from Kim Jong-un, chairman of the Workers' Party of Korea, who had perceived his half-brother as a potential threat to his rule. Although Kim Jong-nam wandered overseas, unable to enter the hermit state, there is no one in North Korea who would kill a bloodline of the supreme leader without an order from Kim Jong-un.

Reportedly, Kim Jong-nam had constantly felt his life was at risk ever since he was pushed aside in the power succession in 2009. Even after Kim Jong-un seized power, he had thought of his half-brother Kim Jong-nam as a potential rival for power over the country. Thus Kim Jong-nam was unable to enter Pyongyang even when his father, Chairman Kim Jong-il died in 2011.

In particular, when North Korea's relationship with China began to wobble after Kim Jong-un seized power, there were endless rumors that China was protecting Kim Jong-nam, which was likely to have made Kim Jong-un nervous.

China was known to have protected Kim Jong-nam to place him at the center of power as an alternative to Kim Jong-un, in case of any sudden changes in North Korea. China is also expected to keep a close eye on the situation concerning Kim Jong-nam's death. Whether Kim's death will affect the relationship between North Korea and China is also an issue of interest.

The China-friendly Jang Song-thaek, who had acted as Kim Jong-nam's guardian in the North, was purged by Kim Jong-un in 2013. Experts believe his death may have been related to the existence of Kim Jong-nam. At the time, North Korea referred to Jang as a "traitor who sought a change of government," and some claim this had something to do with Kim Jong-nam.

Kim Jong-un is likely to have determined that he had to remove the "future threat," Kim Jong-nam, in the process of consolidating his power.

In fact, in 2010 shortly after Kim Jong-un seized power, Kim Jong-nam was threatened by an assassination attempt by North Korea in Beijing, China.

Kim Jong-un and Kim Jong-nam did not seem to be on good terms. Kim Jong-un's complex with his "lineage" probably had some influence. Kim Jong-un's mother, Ko Yong-hui was Korean-Japanese and was Kim Jong-il's third wife, whereas Kim Jong-nam was Kim Jong-il's eldest son and a legitimate descendant of the “Paektu lineage,” who grew up with the love of his father and his grandfather, Kim Il-sung.

One North Korea expert said, "In North Korea, those with power stress lineage. In such an environment, Kim Jong-un was aware of his relative inferiority, so it was natural for him to fear and resent his half-brother while growing up. The fact that a legitimate descendant of the Paektu lineage who could take his place was active outside his control was probably a big threat to Kim Jong-un."

Kim Jong-nam had not been shy in criticizing Kim Jong-un and the North Korean regime, which probably provoked the North. In August 2010, he argued that Kim Jong-un was behind North Korea's failed currency reforms and the ROKS Cheonan incident and revealed that such incidents occurred because his father, Kim Jong-il had tolerated them.

Criticism of Kim Jong-un can also be found throughout the book, My Father Kim Jong-il and I, a collection of interviews with Kim Jong-nam that took place over eight years from 2004 to 2012 by Yoji Gomi, an editor of the Tokyo Shimbun and also a North Korea expert. In an interview, Kim Jong-nam expressed his discontent and concern about Kim Jong-il's choice of Kim Jong-un as his successor. Kim Jong-nam said, "North Korea will collapse if it does not accept the Chinese model and open the country and seek reforms. But if we open the country and seek reforms, Kim Jong-un will fall."

Kim Jong-nam had recently gone into hiding to avoid growing threats to his life. In 2012, his aunt, Kim Kyong-hui, who had visited Singapore for medical treatment, warned him to be careful, mentioning the possibility of an assassination attempt by Pyongyang.
A North Korea expert who chose to remain anonymous said, "The international society is adding more pressure on the North with its human rights and nuclear issues and some are raising the need for a regime change in the North. In such a situation, North Korea may have felt a greater need to get rid of Kim Jong-nam, a potential threat."