Frontline on Tuesday had an episode describing the assassination of Kim Jong Un's half brother.
He was at the airport in Kuala Lumpur, two women rubbed a cloth over his face as a 'prank'.

Long story short, the cloth had VX nerve agent on it.

The time from exposure to death was only a few minutes.

Of course NK denied any involvement, even though their agents were seen in the airport at the time.

Not being a chemical guy, it seems like VX would be difficult to make unless it was state-sponsored.