> If you buy an illegaly obtained human heart, are you not culpable for the death of the former owner?

Not if you do not know that the person has been killed for you to receive the heart or even worse, you ordered someone directly to kill someone. There are plenty of people dying in accidents or of natural causes and some do buy organs (usually bribing doctors) to get ahead in donor waiting lists.

You are culpable for bribing someone and risking that someone might have been killed for the product (at least if you didn't make sure where it came from), thus it is illegal. But you wont be charged with murder.

> If you hire a mercenary to obtaining a human heart, are you completely free from all blame for the subsequent murder?

Well of course you are directly to blame for any of these murders. You ordered it so there's not much of a difference between killing the person yourself and paying someone to do it for you.

So what about the mercenary? If you're directly to blame, is the mercenary innocent? "Just doing his job"?

For me both are to blame for the murder about equally. I believe that in most Western countries the punishment for the mercenary (btw it's an assassin, mercenaries can do legitimate work like providing security in war zones) would be slightly worse.

But I'm not 100% sure about the last point, never had to deal with assassinations so I never felt the need to research it.

I think I can see the problem with his argument. He argues that in judging a person's actions, I should only look at that action in isolation, so as not to hold the person accountable for others' actions.

If I were to look at the isolated action of buying Rhino horn, I could easily argue that no harm is done by trading Rhino horn that has already been cut off a Rhino. But that's not what happens in his argument: He notes that the isolated action of Rhino horn buying is in fact illegal, but ignores that the origin of this rule directly contradicts his moral reasoning.

I do not view a persons action in complete isolation, that's not what I said.

I just say it is a different thing if you kill a Rhino yourself (or order someone to kill one for you) than walking down a market in Hong Kong, seeing some Rhino horn for sale and then deciding to buy it.

Buying the Rhino horn is not legal in any civilised place (because it most likely comes from illegal sources), but the punishment is also not the same one that you would get for walking into your nearest zoo and killing a Rhino yourself, and rightly so.