Malaysian media say the assassination of Kim Jong-nam was a careful operation executed after months of planning, citing a source close to police investigation. 
 
According to the local daily The Star, the source backed this claim with the fact that North Korean chemical expert Ri Jong-chol, who was arrested last week, has been residing in Malaysia for several years.
 
The source also mentioned entry and exit records of North Korean suspects identified by the Malaysian police in the murder of North Korean leader Kim Jong-un's half brother. 
 
Another suspect Hyon Kwang-song, a second secretary at the North's embassy in Kuala Lumpur, arrived in Malaysia last September. Four other North Korean suspects who left Malaysia on the day of the crime on February 13th are also found to have arrived in the Southeast Asian nation between late last month and February seventh. 
 
Malaysian police Chief Khalid Abu Bakar said he believes that they have prepared for the assassination for a considerable period of time. 
 
Multiple sources in Kuala Lumpur say that despite threats to his life, Kim Jong-nam was active on social media, running a Facebook account under the alias "Kim Chol." Sources say this could have helped the suspects to trace his whereabouts. 
 
Meanwhile, a Malaysian man in his 30s was arrested at a condominium in downtown Kuala Lumpur Wednesday night. The police seized chemicals, gloves and shoes at a nearby location. 

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