What Killed Kim Jong Un's Brother?

Organic chemists are a different species (1). While the world was pondering the geopolitical ramifications of the assassination of Kim Jong Un's half-brother Kim Jong-Nam, we were all wondering "what the hell was in those needles?"

This morbid curiosity became even more so as the story changed. Instead of needles, different reports said that a liquid was either sprayed in Kim's face or applied with a cloth. For us chemists, that is even crazier. What on earth could be applied to the skin and cause dizziness, a headache, and then death so quickly? This has led to speculation about what chemical was used, because, given the "facts" that we now have, there is no obvious answer. 

This didn't stop me from trying to figure it out, even knowing in advance that I'd almost surely be wrong. But at least I'll be wrong first. After a few hours of research, I came up with the table below: some common poisons, and why they may or may not be reasonable candidates (2). Are they sufficiently toxic to kill someone, and so quickly? Will the penetrate the skin (3)? Do they have to? Do the symptoms caused by these poisons match those reported in the news? Here:

So, whatever the assassins used, it was obscure enough that the best I could come up with was kale, which is unlikely to be correct. So, you've wasted ten minutes reading this while I wasted two hours writing it, and arguably the five years it took to get the Ph.D. Maybe culinary school would have been a better choice. Or not. I would have failed kale. Yep- a kale fail.

Notes:

(1) The term "mutants" has been used. And not necessarily unfairly.

(2) The table is based on the assumption that the poison was applied, not injected.

(3) Some poisons that can't penetrate skin can be to do so by dissolving them in a solvent that readily does. A sodium cyanide solution in water will not harm you, but a solution in dimethyl sulfoxide (DMSO) can.