The chemical substance used to kill Kim Jong Nam was VX nerve agent, according to a preliminary report by the Chemistry Department of Malaysia, Malaysian police said in a statement Friday.

North Korean leader Kim Jong Un's brother Kim Jong Nam

Nerve agents are the most toxic and fast-acting substance known in chemical warfare -- and VX is the most potent of all of them, according to the US Centers for Disease Control and Prevention.

"If it's inhaled as a vapor, (the victim) very quickly becomes what is called, crudely, a body flopper. You'll be on the ground with your arms and legs twitching unable to breathe," former United Nations weapons inspector David Kay told CNN in 1998. "You will lose control of your stomach. It's not a very pleasant way to die."

It works by inhibiting the operation of an enzyme that helps the body's nervous system function, according to the Organization for the Prohibition of Chemical Weapons (OPCW).

Kim, the half-brother of North Korean leader Kim Jong Un, died February 13 before he was scheduled to board a flight from Kuala Lumpur to Macau.

The Royal Malaysian Police say that two women approached him from behind and wiped his face with some sort of substance./.

VNF (According to CNN)