FILE - In this May 4, 2001, file photo, a man believed to be Kim Jong Nam, the eldest son of then North Korean leader Kim Jong Il, walks out of a police van before boarding an airplane heading to Beijing at Narita international airport in Narita, northeast of Tokyo. Kim was assassinated at an airport in Kuala Lumpur, telling medical workers before he died that he had been attacked with a chemical spray a Malaysian official said Tuesday. (AP Photo/Shizuo Kambayashi, File)

KUALA LUMPUR, Malaysia (AP) -- The astonishing assassination of North Korea leader Kim Jong Un's half-brother rippled across Asia on Wednesday as Malaysian investigators scoured airport surveillance video for clues about the two female assailants and rival South Korea offered up a single, shaky motive: paranoia.

Kim Jong Nam, 46, was targeted Monday in a shopping concourse at Kuala Lumpur International Airport, said a senior Malaysian government official, who spoke on condition of anonymity because the case involves sensitive diplomacy. He had not yet gone through security.

Kim, who died on the way to a hospital, told medical workers before he died that he had been attacked with a chemical spray, the official said.

South Korea's spy service said Wednesday that North Korea had been trying for five years to kill Kim Jong Nam. But the National Intelligence Service did not definitely say that it was North Korea, just that it was presumed to be a North Korean operation, according to lawmakers who briefed reporters about the closed door meeting with the spy officials.

The NIS cited Kim Jong Un's alleged "paranoia" about his half-brother. Still, the NIS has a history of botching intelligence on the North and has long sought to portray the North's leaders as mentally unstable.

In Malaysia, police were searching for clues in the CCTV footage from the airport, said Selangor police chief Abdul Samah Mat. The airport is in Selangor near Kuala Lumpur.

Kim Jong Nam was estranged from his younger brother, the North Korean leader. Although he had been tipped by some outsiders as a possible successor to his dictator father, others thought that was unlikely because he lived outside the country, including recently in Macau, Singapore and Malaysia.

He reportedly fell further out of favor when he was caught trying to enter Japan on a false passport in 2001, saying he wanted to visit Tokyo Disneyland.

Multiple South Korean media reports, citing unidentified sources, said Kim Jong Nam was killed at the airport by two women believed to be North Korean agents. They fled in a taxi and were being sought by Malaysian police, the reports said.

A Malaysian police statement confirmed the death of a 46-year-old North Korean man whom it identified from his travel document as Kim Chol, born in Pyongyang on June 10, 1970. "Investigation is in progress and a post mortem examination request has been made to ascertain the cause of death," the statement said.

Ken Gause, at the CNA think tank in Washington who has studied North Korea's leadership for 30 years, said Kim Chol was a name that Kim Jong Nam has traveled under. He is believed to have been born May 10, 1971, although birthdays are always unclear for senior North Koreans, Gause said.

Mark Tokola, vice president of the Korea Economic Institute in Washington and a former deputy chief of mission at the U.S. Embassy in Seoul, said it would be surprising if Kim Jong Nam was not killed on the orders of his brother, given that North Korean agents have reportedly tried to assassinate Kim Jong Nam in the past.

"It seems probable that the motivation for the murder was a continuing sense of paranoia on the part of Kim Jong Un," Tokola wrote in a commentary Tuesday. Although there was scant evidence that Kim Jong Nam was plotting against the North Korean leader, he provided an alternative for North Koreans who would want to depose his brother.

The reported killing came as North Korea celebrated its latest missile launch, which foreign experts were analyzing for evidence of advancement in the country's missile capabilities. For the next several days, North Korea will be marking the birthday of its late leader Kim Jong Il, the brothers' father, though they have different mothers. The major holiday this Thursday is called the "Day of the Shining Star" and will be feted with figure skating and synchronized swimming exhibitions, fireworks and mass rallies.

Since taking power in late 2011, Kim Jong Un has executed or purged a slew of high-level government officials in what the South Korean government has described as a "reign of terror." The most spectacular was the 2013 execution by anti-aircraft fire of his uncle, Jang Song Thaek, once considered the country's second-most-powerful man, for what the North alleged was treason.

Story continues