Following his visit to the resort island Langkawi, Kim Jong-nam arrived at terminal 2 sometime before 9:00 a.m. to take a 10:50 a.m. AirAsia flight to Macau.

[13][21] Kim's extensive Facebook use under this pseudonym since at least 2010, and use of commercial email services for communications, may have made it easier for North Korean agents to seek his whereabouts and track his movements.

[23][24] On 15 February, Malaysian police arrested 28-year-old Vietnamese woman Đoàn Thị Hương at Kuala Lumpur International Airport in connection with the attack.

[23][28] Hương told the police that she was instructed by four men who were traveling with them to spray Kim with an unidentified liquid while Aisyah held and covered his face with a handkerchief as part of a prank.

A book by Anna Fifield, The Washington Post bureau chief in Beijing, had earlier reported this, stating he had been previously filmed abroad with a US intelligence agent, and had carried a backpack that contained $120,000 in cash.

[28] The autopsy was conducted by pathologist Mohamad Shah Mahmood of Kuala Lumpur Hospital, who testified that Kim's lungs, brain, liver and spleen were affected by the poison.

[49][50] On 24 February, Malaysia's police chief Khalid Abu Bakar announced that a post-mortem toxicology report had found traces of the nerve agent VX on Kim's face.

[51][52] This method could ensure that the assailants were not themselves killed by the poison, which can be fatal in very small amounts; additionally, smuggling the chemical components into Malaysia separately could have helped avoid detection.

VX degrades rapidly in storage and North Korea's supplies are believed to be several years old, which could explain the apparent weakness of the chemical.

[60] Kim Jong-nam's blazer, backpack and watch were initially submitted to a police chemistry department for analysis, but subsequently returned to officials from the North Korean embassy.

[61] The ambassador said they would reject the outcome of the post-mortem conducted "on its citizen without permission" and perceived the decision as a "violation of human rights" and thus would lodge a complaint to the International Court of Justice (ICJ).

[66] The North Korean government rejected all findings, accused the Malaysian police of fabricating evidence in collusion with South Korea and demanded the release of the three people being held in connection with the death.

[79]In a joint press conference in Tokyo, Japan, he said: "We hoped for a successful outcome from the historic meeting",[80] adding that "Malaysia will re-open their embassy in North Korea as an end to the diplomatic row over the assassination of Kim Jong-nam".

[88][87] A lawyer for Hương requested a second autopsy as he doubted Malaysian expertise, calling for experts from Japan and Iraq as well pathologists from North Korea itself to be involved.

[103] While in transit through China, he told the media that the Malaysian police threatened to hurt his family if he did not confess his involvement in the murder and said his arrest was part of a "conspiracy".

[113] The murder trial of Siti Aisyah and Đoàn Thị Hương began on 2 October 2017, at the High Court in Shah Alam, Selangor, Malaysia, with both pleading not guilty.

[119] Another chemical pathologist, Nur Ashikin Othman, told the court that Kim had very low blood levels of cholinesterase, the enzyme inhibited by anticholinesterase agents such as VX.

[119][121] Toxicologist K. Sharmilah testified that vials of atropine, a drug used as an antidote to poisoning with nerve agents such as VX, were found in Kim Jong-nam's bag.

[122][123] On 8 October, the trial had to be moved to a high-security laboratory due to the danger posed by the nerve agent-tainted clothing admitted into evidence.

[128]During the cross examination, the defence lawyer also produced an affidavit Thủy had made the previous October that also contained her police statement.

[128][129][130] The lawyer also told that in November he had asked the Malaysian attorney general's office for assistance in convincing Thủy to travel to Malaysia to testify about her role in introducing Hương to the North Korean man.

[131][90] Through the trial from 20 March, Hisyam screened a video of CCTV recorded at Noi Bai International Airport on 2 February 2017, on her client played a prank on a Vietnamese government official named Trịnh Ngọc Linh in Hanoi less than two weeks before the attack, which showed her approaching the man from behind and putting her arms around his neck.

[137] The Malaysian police investigator however deny the blame that with the absence of four North Korean suspects their investigation had caused prejudice, insisting that "as for the case, the main perpetrators who committed the killing are the two accused", as well denying on the accusation that Malaysian police did not take adequate measures to pursue the four men, stressing that Interpol had issued an alert for the four men to be arrested based on Malaysia's request.

[140] On 16 August, the Malaysian court has decided to continue the trial on 1 November until April 2019,[141] with the judge saying that "a political assassination cannot be ruled out" although there was not enough evidence to say, adding that security camera footage "showed that they had the knowledge that the liquid on their hands was toxic and there was no hidden crew and no attempt to bring the person in on the joke afterward, as is common in reality TV prank shows".

[154] Despite similar callings from the Vietnamese government to release Đoàn Thị Hương in the manner of the Indonesian suspect,[155] Malaysian prosecutors rejected the request and said the trial would continue to proceed with a postponement until 1 April due to Hương's poor health and psychological condition—she had not slept for three nights following the Malaysian attorney general's decision to drop the charges against Aisyah.

[156][157] Hương's defence lawyers felt the Malaysian government was practicing discrimination in the judiciary system since the court previously stated that it found a prima facie case against both suspects but only released one.

Ramkarpal felt that Thomas's refusal to withdraw the murder charge against the second suspect was "mind boggling and raises questions about the powers of attorney general in the country".

[159][160]Vietnamese Foreign Affairs Ministry spokeswoman Lê Thị Thu Hằng regretted the Malaysian attorney general's decision and called for a fair trial on the case.

[164][165][166] Bridget Welsh, a Southeast Asia expert with John Cabot University, predicted that the decision will risk a "thorny bilateral problem with Vietnam if there is no similar treatment towards their citizen".

[167] Malaysian Chinese Association (MCA) President Wee Ka Siong expressed concern over possible meddling in the trial outcome.