Death Note: L, Anonymity & Eluding Entropy

Depends on the assumptions you make, I think. If we make the assumption that #2 and #3 obtained Death Notes at a known time, then any observations before then still pin down #1 - if there are kills at morning Japan-time, that serves to pin him down to Japan, etc.

But once #2 and #3 become equally active, now any evidence like that serves to narrow down the propositions 'any of #1, #2, #3 are in Japan', so if someone asked you what's the odds that #2 lives in Japan, you would only have 1/3 the evidence you did before - because any kill linked to Japan would only have 1/3 chance of having been #2. If a kill is made using information from a rural Iowan newspaper with circulation of 100, well, all you know is that any of 1/2/3 had access to it (and maybe all 3!). And so on.

(In bit terms, if there were 4 Death Note users, then any observation has 1/4 the power it did, or 1/2^2; similarly, if there were 16 users, or 32 users... Once you established someone was a Death Note user you would still need to do that many more bits of work to figure out which Death Note user you want.)

Japanese TV show and comic book about a school boy who writes names into a notebook given to him by an angel of death. Writing names in a notebook kills them.

I'm not sure why it's on hacker news-- so I called them tv shows and comic books to offend the otaku.

"Death by ironic circumstances. Time of death chosen from within the allowed range such that hazards to bystanders are minimized, then such that irony is maximized, then randomly."

Solving for maxima in the Law of Universal Perversity should do it.

How much can you trust each bit of information you gained though? For example, it might be very possible that Light could be intentionally waking up at the middle of the night to do his killings. In which case you would've ruled out japan, which then ruins your subsequent analysis which is all somewhat based on him being in japan. Verifying every bit of information gained or even assigning a probability to how much you can trust it seems to be a hard problem.

It's kind of funny that you posted this now, because at the moment I'm actually hacking on the last level of Stripe's Capture the Flag with Low of Solipsism, L's theme, Kira's theme, Near's theme, and Zetsubou Billy looping in the background.

As a side note, has anyone else considered the possibility that it's entirely possible that Light could have simply set up a server which would schedule his victims' deaths for a certain randomised time, then at that time pull up an image of them on X and print their name on one page of the death note which was set up to be indefinitely recycled within the same printer?

At that point it'd have been trivial for him to set up a simple password-protected REST interface which would accept POST requests of victims' names/pictures, and he could have even done all his future recruiting through Tor without taking the risk of using physical mail (and eventually facilitating the recruitment of a local "Kira" in every country, possibly vetting through social media comment histories in a similar fashion to the way he evaluated Mikami).

This setup wouldn't necessarily have been possible, but the wording of the Death Note looks like it might have allowed for it (contingent on how strictly it defined "mind"). At the very least, printing through electronic media would have been worth an experiment.

Assuming the server were reasonably secure, and he'd taken appropriate steps to scale as time passed, the very fact of all that ink on one page would have made it completely illegible, and thus inconclusive evidence. Then, he could have just performed any Kira actions from a virtual machine with an encrypted filesystem, eventually ceasing any direct killings as his army increased in size. It would have scaled beautifully, and he'd have been almost perfectly anonymous.

To put the icing on the cake, if he didn't want to put in so much grunt work, he could have simply configured his server to automatically hook into every well-maintained reputable public listing of convicted violent criminals (as well as listings like the website of America's Most Wanted) and then forgotten about the whole thing. And hell, if the whole thing is automated, why not just put in a line of code that marks each death as being at the hands of the most likely intelligence agency? It would have achieved the same chilling effect ("OMG THE CIA IS KILLING EVERY CRIMINAL IN THE WORLD NOW!"), and thus the same goal, without even realistically risking his own livelihood.