The daily cited an unidentified "person knowledgeable about the matter" for the report.
Former US officials tell the Journal that Kim Jong Nam was being eyed by countries including China as a potential replacement for his half-brother, though American agencies determined he was "ill-suited" for the role.
The CIA declined to comment to The Journal.
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.
The former officials also said Mr Kim had been nearly certainly in contact with security services of other countries, particularly China's, the Journal said.
South Korean and USA officials have said the North Korean authorities had ordered the assassination of Kim Jong-nam, who had been critical of his family's dynastic rule.
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Based on interviews with 610 escapees from Kim Jong-Un's dictatorship, the authors claim they mapped 323 reports of state-sanctioned killings across 318 sites.
The fact that the CIA held meetings with Kim Jong-nam illustrates the lengths United States intelligence will go to gather information about the hermetic country. He reportedly met with an American intelligence agent in the days before he was killed. He had been living overseas for years but could have been seen as a threat to Kim Jong Un's rule.
It's extremely hard for outside governments and media to verify information about North Korea and members of its secretive ruling family because Pyongyang closely watches visitors and enforces a stringent information blockade on its citizens.
After his murder, North Korean dissidents rushed his son, Kim Han Sol, and other family members out of Macau and into hiding, where they remain.
South Korea's Chosun Ilbo newspaper reported last month that Kim Hyok Chol was sentenced to death for "betraying the Supreme Leader" after he was "won over by the US" during pre-summit negotiations. Kim claimed he fell from grace after gaining a reputation as a reformer, which Kim Jong Il deemed unacceptable.
One defector held in a labour camp in the early 2000s described how 80 inmates were made to watch the killing of three women charged with trying to escape to China.