A person "knowledgeable about the matter" told the Journal that Kim met agency operatives several times before he died.
Two women were charged with poisoning Kim Jong Nam by smearing his face with liquid VX, a banned chemical weapon, at Kuala Lumpur airport in February 2017.
But, North Korean officials continue to say the exact opposite, warning they will not give up their weapons unilaterally and setting an end-of-the-year ultimatum for the United States to change its approach.
Soo Kim, a policy analyst at the Rand Corp. and former Central Intelligence Agency analyst, said North Korea was following a "well-rehearsed playbook", involving dramatic, inflammatory rhetoric, placing the blame on Washington for the breakdown in talks, missile launches, playing hard to get, and arm-twisting Seoul. "It said his backpack contained $120,000 in cash, which could have been payment for intelligence-related activities, or earnings from his casino businesses".
Kim Jong-nam, who lived in exile in Macau before he died, was reportedly viewed as a threat to the rule of his younger brother.
South Korean officials said Kim Yo Jong, who has emerged over the past 18 months as a top aide to her brother, did not have any particular message or letter for South Korean President Moon Jae-in.
Former officials said that he had nearly certainly been in contact with security services from other countries, particularly China's, although he had no known power base in Pyongyang and had not lived in the country for several years.
Trump also reiterated his good relationship with Kim as well as the tremendous potential of the DPRK.
Since a second summit in Vietnam collapsed without a recommitment to the general goals outlined in Singapore, North Korea has complained of U.S. sanctions and Kim Jong Un said he would wait until the end of the year before deciding on whether to take a "new path".
Kim gained a reputation as somewhat of a playboy when studying overseas, and lost his father's support after being arrested trying to travel to Disneyland in Tokyo on a fake Chinese passport.
Once seen as leader Kim Jong Il's successor, Mr Kim Jong Nam apparently fell from grace after being deported from Japan in 2001 for trying to enter on a forged passport.
"Today we are seeing off a great person who dedicated her entire life to women", South Korean president Moon Jae-in, now visiting Finland, said in a statement.
During the women's trial, police said Kim had spent several days on the island of Langkawi, where he met a Korean-American man at a hotel.
US President Donald Trump and Kim Jong-un have met twice, in Hanoi in February and Singapore in June past year.