Thanks for the reply. You might want to hide the spoilers, though.
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That's a good point about only knowing the last victim being a danger.
I assumed those instructions about barring people from knowing the case came from Richard, left behind along with his work. Otherwise, wouldn't others knowing enough about it to give those instructions also be in danger of triggering the curse? It would explain how they could have known to hire a recluse like Richard and even keep his name secret, but how would they have gained that knowledge in the first place without significant exposure risk themselves, and isn't the fact that Richard happened to know that last victim the only reason he was able to serve his purpose? But how could they have known that he did without themselves also knowing the last victim?
Now that I think about it, it even seems kind of contrived that Richard not only had the kind of occupation to let himself be hired for this kind of thing and was enough of a recluse to prevent the curse from spreading by not knowing many people, but somehow one of the few people he did know just happened to be the last victim.