The police reconstruction of Kim Jong-nam's killing was captured in grainy footage.
The case has also sparked a diplomatic row between Pyongyang and Kuala Lumpur, after Malaysia rejected North Korean demands for the body to be handed over to them immediately.
Two women, one of them Indonesian and the other traveling on a Vietnamese passport, and a boyfriend of one of them, have been arrested earlier on suspicion of involvement in the death of Kim Jong Nam.
Jong-Nam was treated there and transferred by ambulance to hospital but died during the journey.
Pyongyang has made no comment on the killing, but its diplomats objected to the post-mortem being carried out, a senior Malaysian official familiar with the investigation told AFP.
Officers have already arrested one North Korean, a Malaysian man and a Vietnamese woman, as well as an Indonesian woman.
Kim Jong Nam had spoken out publicly against his family's dynastic control of the isolated, nuclear-armed North Korea.
Police said the North Korean man's work permit had expired February 6, a week before Kim's death.
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"We believe the North Korean regime is behind this incident considering five suspects are North Koreans" Jeong Joon-hee, spokesman at the South Korea's Unification Ministry that handles inter-Korea affairs, told a briefing. "We have only received the application from the North Korean embassy yesterday", the police chief said.
Asked about the assumption, Noor Rashid replied: "I think there is footage being released. and you can interpret from the footage".
"We have to send a sample to the chemistry department, we have to send a sample for toxicology tests", Noor Rashid said.
Kim Jong Nam, the elder of the two, did not attend his father's funeral. He is believed to have two sons and a daughter with two women living in Beijing and Macau. They say they would release the body to the next of kin, but so far, Kim's next of kin have not come forward.
"We are still waiting for the next of kin application, we have not received it yet".
It has also accused the country of "colluding with outside forces" - a veiled reference to South Korea.
Kang Chol, North Korea's ambassador to Malaysia, said Malaysia was probably "trying to hide something", noting that the autopsy was carried out "unilaterally and excluding our attendance".
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