For the first mystery, I don't think that the horn's been moved. I think that the pillar has a false bottom (or false top) and that if you open it without the keys, you'll see whatever's in the second compartment. I think that the Kirin's Horn is still on it's statue, hidden within the pillar, and everybody's looking at a fake Kirin statue. Who could have a fake statue made? Good question...
As for the second mystery, Ther's only one person in that room who'd see Conan as a threat instead of an annoyance (Nakamori), a challenge (KID), a friend (The DBs), or a facinating character in the chase after KID (the film crew). I think we all know who that would be...
Finally, the postscript on the notice (supposedly from KID) says "We're done with the child's play. We shall do battle as adults." The guy who's developed a reutation for treating the police as children sends a note saying that. Riiiiigghhttt... This isn't a challenge from Kaito Kid, it's a challenge to Kaito Kid!
I don't know what wild hair's gotten up Jiroki's behind this time, but it's clear (to me at least) that he's behind this whole mess; sending a challenge letter to himself, Rigging the Kirin's horn to set up a fake mystery (so he can 'solve' it of course), zapping Conan so he can't solve it before Jiroki can figure out who KID's disguising himself as. I can't prove any of this, of course, but he's the only one with the method (Cash), motive (Vainglory), and opportunity (a month's preparation, apparently before he even got the 'challenge').
As for who KID's disguising himself as, I'll say that i's Nakamori-Keibu. I's not that I don't like the idea of it being Haibara's hat, but this way, when she solves the case, Jiroki will feel like even more of a fool.






