The Malaysian police's investigation into the murder of the North Korean leader's estranged half-brother was "shoddy" and could result in an unfair trial, a court heard yesterday.

Defence lawyers for two young women -- Indonesian Siti Aisyah and Vietnamese Doan Thi Huong -- charged with the Cold War-style killing of Kim Jong-Nam sought to discredit the manner in which the police conducted their probe.

Kim, the estranged half-brother of North Korean leader Kim Jong Un, was poisoned at Kuala Lumpur's international airport in February last year while he was about the take a flight to Macau.

The women are on trial for allegedly smearing the banned nerve agent VX on the face of Kim, who died in agony minutes later. Kim had been living in exile since a family fallout.

Defence lawyers have argued that the women were recruited to take part in what they thought were prank TV shows but were instead tricked into becoming inadvertent assassins, in an elaborate plot by a group of North Korean agents.