According to a statement by Malaysian police on Saturday, the suspect was arrested a day earlier in Selangor state and was identified as 47-year-old Ri Jong-chol from North Korea.
On Wednesday, a 28-year-old woman named Doan Thi Huong and carrying Vietnamese travel documents was arrested at Kuala Lumpur International Airport, the scene of Monday's poisoning.
Two others were also detained in relation to the incident: A 25-year-old Indonesian woman called Siti Aishah, and a man who was accompanying her, reportedly a Malaysian national.
Police are also searching for other suspects including four men, who are believed to be involved in the case.
Kim Jong-nam was on his way to the Chinese territory of Macau, where he had been reportedly residing under China's protection.
The 46-year-old was targeted in the shopping plaza at the airport and had not yet gone through passport control, a senior government official said.
A second autopsy on the body will take place on Saturday after Wednesday's first autopsy was reportedly inconclusive, a senior Malaysian official said.
However, Selangor state police chief Abdul Samah dismissed reports that a second autopsy would have to conducted.
"The Malaysian side forced the post-mortem without our permission and witnessing," North Korea's ambassador Kang Chol said after Malaysian police rejected demands made earlier in the week to return the remains.
"We will categorically reject the result of the post-mortem conducted unilaterally excluding our attendance."
Malaysia hit back by saying the country's rules must be followed.
"While in Malaysia, everyone has to obey and follow our rules and regulations. That includes North Korea," Inspector General Tan Sri Khalid Abu Bakar, told a local news agency.
On Saturday, Indonesian police said that the Indonesian detained suspect, Aishah, thought that she was allegedly taking part in a reality television prank.
"She was probably just used without realising it was an assassination attempt," Indonesian Police Chief Tito Karnavian said according to local media.
He had said on several occasions over the years that he had no interest in leading North Korea.
Source: Al Jazeera and news agencies