Or obscuring the source. If I wanted to cause a Chinese-North Korea conflict, I'd do it in a way that gives me enough time to tie up loose ends and points in a certain direction.

Same with Litvinenko. We will never find out the true story. Was it a message? Probably. But from who to who? Might have been FSB, but there were plenty of other parties that really didn't like Litvinenko and could have used Russian Polonium either to blame the FSB or to tell the FSB not to fuck with them, because they had the means to blame them for random hits (or a million other possible reasons).