Oh my God, it was you?!? I can't believe that Jasmine would do that!
Oh wait, I did know

I find it funny that nobody suspected Jasmine, when in the past few games, Jasmine was one of the biggest suspects.
My clues and stuff
Philby - a tree branch. Koda tries to get Kenai down with a tree branch (or stick. Something like that) when they first meet, and Kenai is stuck in a trap.
White Rabbit - a lit metal lantern. Well, it sort of mixes with Big Thunder Mountain. The lantern is supposed to represent the Northern Lights, or the Spirits in the movie. The place Kenai is trying to get to is where the lights touch the mountain. Therefore, it's a lantern on Big Thunder Mountain.
Mad Hatter - Piece of paper with words "Easter. Low. Key. Shan". It's an oronym! Or a homonym, one of the two. Say it all out loud, and it should sound similar to "It's the location". This refers to the location of the murder, being Country Bear Jamboree. No further explanation necessary.
Random note, people were saying that the death of Philby meant it was a random-thread goer. Let me say, the reason I chose him wasn't for whatever you guys were thinking, but because he managed to survive all the way through the last MM, and was a main poster in that game. Better to kill someone who enjoyed the previous game unharmed, than someone who's playing for the first time.