I think Kaitou Kid (and Jii) might be on the train in disguise as room D's occupants. I thought they were case culprits because the should have ran into the string, but now they have been cleared of any role they are suspicious. First Conan accused the maid of running awfully quickly like she did sports. Second he got really close to accusing them of not mentioning the string because they didn't want to get involved in the case. Third, when all the suspects fled completely panicked at the fire, room D's occupants remained where they were until Conan told them to get a move on when they should have been terrified of fire because of their pasts like Vermouth said. The thieving duo would know a fake fire when they see one because of the stage tricks.
I don't think Kaitou Kid would have a clue what is going on with the Black Org, but he might chip in a smoke bomb at the end or something like that if he sees suspicious people with guns and make some mayhem to allow Conan and crew to escape.
Edit: ⇩ lol, Detective Kudo posted the same thing at the exact same time...