Malaysia‘s senior police officials said Sunday they are looking for four more North Korean suspects linked to the mysterious murder of Kim Jong-nam, the estranged half-brother of North Korean leader Kim Jong-un.

Malaysia’s deputy national police chief Noor Rashid Ibrahim said in the press conference that the authorities identified all four suspects, who he said had left the country on Feb. 13 -- the same day when Kim Jong-nam died after being attacked with poison by two women at Kuala Lumpur airport.

The suspects were named Ri Ji-hyon, 32, Hong Song-hac, 34, O Jong-gil, 55, and Ri Jae-nam, 57, the police chief added. He also identified a fifth person of interest, named as 50-year-old Ri Ji-u, and showed pictures of two North Koreans wanted by the government but not identified by name.

The revelation came amid the speculation that Kim Jong-nam was assassinated by North Korean agents under the instruction of Kim Jong-un who has long viewed his flamboyant, outspoken elder brother as a threat to his dictatorial power.

When asked by the reporters whether the communist regime was behind the killing, the deputy chief said “the suspects are all North Korean,” indicating that Pyongyang played a significant role in what South Korean officials described as “assassination.”

“We believe North Korea is behind the murder of Kim Jong-nam,” Jeong Joon-hee, spokesman at Seoul’s Ministry of the Unification, said on Sunday after the press conference. ““North Korea has conducted criminal, terrorism activity against humanity.”

Earlier in the day, The New Straits Times, an English-language newspaper in Malaysia, quoted an unidentified senior police official as saying that the investigator had “solid” evidence that can draw the death of Kim Jong-nam to a North Korean citizen identified as Ri Jong-chol who was arrested on Saturday.

The fourth suspect to be detained in connection to the death of Kim, Ri was apprehended at an apartment located in downtown Kuala Lumpur. When being arrested, he was carrying an “I-Kad” — an official identification card issued to foreign workers — that said his name is Ri Jong-chol.

The newspaper reported that Ri could be an operative of the North Korean Reconnaissance General Bureau which manages the communist state’s clandestine operations, saying the place he was arrested had been used as a “safehouse” for North Korean agents in Malaysia since 2011.

The Malaysian police has also been trying to ascertain the authenticity of Ri’s identification card, which has low security features and could be easily forged, said the newspaper. The police are investigating into the possibility that he forged the document to hide his real identity.

“Unless they are high-profile officials and secret agents, it is unlikely to live abroad independently,” said a South Korean official familiar with North Korea’s intelligence operation. “It is quite likely that Ri was assigned a special operation.“

Ri is the fourth suspect to be detained in the death of Kim, who died on his way to hospital within minutes after being sprayed with poison by two women as he waited to board a flight at Kuala Lumpur International Airport.

The two women -- identified as 28-year-old Vietnamese Doan Thi Huong and 25-year-old Indonesian Siti Aisha -- told the police they thought the attack was part of a comedy show prank and rehearsed the scene to get it right for the video.

Tito Karnavian, Indonesia‘s most senior policeman, said the two women had already performed the prank on other men before attacking Kim. It involved convincing them to close their eyes before spraying them with water.

”Such an action was done three or four times and they were given a few dollars for it, and with the last target, Kim Jong-nam, allegedly there were dangerous materials in the sprayer,“ Karnavian told reporters on Friday

One Indonesian newspaper reported that Aisha was approached by a mysterious man at the Kuala Lumpur nightclub and offered $100 to be involved in a prank. Her 26-year-old Malaysian boyfriend was also arrested by police as an alleged accomplice. Police are hunting for other alleged accomplices.

North Korea, meanwhile, has accused the Malaysian government of conducting a “hostile” investigation against the reclusive regime, saying that they would reject the outcome of autopsy on the body believed to be Kim Jong-nam.

In his first public statement on the case, North Korean Ambassador to Malaysia Kang Chol said that North Korea would “categorically reject” the results of the autopsy, which he said was performed despite its objections and with its officials excluded.

“The Malaysian side forced the postmortem without our permission and witnessing, we will categorically reject the result of the postmortem conducted unilaterally excluding our attendance,” Kang said

The ambassador also called for the body, whose identity he did not mention, to be released immediately because the deceased was traveling on a diplomatic passport and therefore should be under North Korea’s consular protection.

Earlier Friday, Malaysian police said that the body would not be handed over to the North Korean embassy until a family member could supply a matching DNA sample. So far, no family member or next of kin has come forward to identify or claim the body, according to the Malaysian police.

By Yeo Jun-suk  (jasonyeo@heraldcorp.com)