"I'm writing a book..." (c)
Somewhere in the Pacific, in the international waters, and by that I mean in the waters themselves, not on a ship, John killed Jack.
1) No one saw it happening, but a few hours laters, still in the international waters, some fishermen found the body. The body was easily identifiable and had a passport with it, thus clearly stating the citizenship of the deceased. Where should the fishermen report the incident? Who will investigate the crime? Who will hold the trial?
2) No on saw it happening, but a few days later, still in the inernational waters, some fishermen found the body. The body was unidentifiable/had no id/the deceased had no citizenship of any country. Same questions.
3) John didn't kill Jack, but rather performed a clearly offencive and punishable act, which didn't violate any of Jacks universal human rights (can't come up with one right now... broke his nose, maybe?). Same questions (replace fishermen with Jack, of course).
4) Same as above, but neither of our heroes had a citizenship.
5) Ok, that's outright weird, but still: some fishermen find a dead body, no id, no way to identify. An investigation occurs. Autopsy reveals, that the death was natural, but after the death some of it's internal organs were removed. Again, same questions.
Yes, I understand that the most probable answer to these questions would be "No one would care", but let's presume that the investigation is inevitable (the fishermens' boat was crowded with journalists and high-grade politicians, for example).
Thank you for your time.