It's a changeling. It's got to be. One of those ponies is a changeling who's been screwing with everypony there.

Only question is who is it? I'm going to go with Fleetfoot being a changeling in disguise and screwing with everyone to create a situation where nothing will get done, before making the kill attempt. It's not Fluttershy because she was attacked by 'Rainbow Dash', it's not Rainbow Dash, Shining, or Rarity because they were impersonated, it's not Pinkie Pie being an unreliable narrator because she had the blade stolen off of her, Maud, Octavia, Soarin and Fleur have each tried to counter-act the changelings attempts to create chaos, meaning it probably isn't them.

That's my theory.

I think that it's Fleur. Most likely using some type of disguise spell. I'm pretty sure that she once asked Pinkie about the knife in the library, but didn't offer her help, which would have made more sense than "Shining" offering his help. And I have a strong instinct for it. Probably extremely wrong.

Alright time to think who could of be.

DAH! Obviously a changeling is involved, but it's no easy matter to determine which one it was. Again, your third will be the hardest. By the way, how long do we have until the answer gets published?

4651515 the picture now shows cheese sandwich playing his accordian with a smile on his face next to pinkie and derpy on the ground sitting next to filthy rich

4716939 This time Filthy rich, Spitfire flying a bit above her with derpy clumsily passing by and Aj wrapping her hoof around pinkie

4716985 you forgot cheese sandwich

4717031 This time Filthy rich, Spitfire flying a bit above her with derpy clumsily passing by, Cheese sandwich throwing confetti at Aj wrapping her hoof around pinkie. There.

Fluttershy is a changeling and murderer.

There have been instances of fluttershy doing strange things up until now and acting OoC, but I have dismissed them as red herrings in the previous cases.

Looking back, in the second chapter, when Fluttershy asks the master mind "What did we do to deserve this?" and the Master Mind, who has been truthful but has a habit of utilizing exacting-wording truth, strangely replies "Oh, Fluttershy, you're simply a means to a end." instead of addressing the plurality of the sentence."

Plus, Discord looked sad. So that means that either Fluttershy has always been a changeling, or the real one was replaced at some unknown time.

Plus, Pinkie said Fluttershy smells nice, which seems odd seeing as Fluttershy should smell nothing or sterile given that she's manning the infrirmary, and I think if Fluttershy could barely handle and freaks out about some of the things that have happened (being accused of getting the charts wrong, etc.) then she would have essentially went catatonic at Applejack's death.

Plus, Pinkie told Fluttershy that she was going to her room, and Fleetfoot was waiting for her. "Fluttershy" was quite literally the only persona who knew Pinky was there.

If its not a changeling, then Twixie has been posing as Fluttershy via illusions to do so--either willingly or being forced to do so.

Upon reflection, I believe that she may also be Chyrsalis. The way Pinkie describes the waiters being glass-eyed and slack-jawed is exactly how Shining Armor is depicted when he was under Chrysalis's thrall in the Canterlot wedding episode of the season 02 finale. While conceivably any Changeling could charm someone, I think only the queen would have enough juice to mojo the entire staff at once.

4716586 I usually publish the trial 3 days after the investigation part, so around Monday I think

4717582 HOLY SHIT DUDE THAT IS AN INTERESTING THEORY!

A somepony who shot a fire at a princess, obviously the best possible suspect is unicorn. Who would do that? Shining, Fleur or Rarity? ( They couldn't teleport, but still could use their telekinesis )

And there's no way anypony other than unicorn could loop a rope through a pillar with a mere hoof. It had to be somepony with a horn and magic or maybe somepony with knowledge of prongs from Pinkie which is Fleur. They couldn't possibly wield the dagger with a hoof as well as throwing a strong earth pony like Applejack through the window ( or maybe just because she's weakened from bloodloss while crawling away that she's an easy target )

It narrows the possible suspect to those three.

But for my theory, and I think it's Rarity herself. ( Or maybe Fleur, but not Shining or maybe he is? )

She's after all a master when it comes to illusion magic and master actress to bend somepony to her will. Like with Spike, so it couldn't be Shining whose specialty is defensive magic and Fleur who always act composed and I don't think I ever saw her knew about any magic beyond leviation as well never committing a murder back in the mansion.

Plus, there is, the hint ; Five : Behind the face of a friend Obviously somepony Pinkie knew very well ( Or it's maybe a hint on the masterminds identity being one of them....again, there's after all an empty slot. It may not the culprit )

Five : Meaning the five impostors from the previous chapters ( Doppelgangers of Pinkie, Maud, Rainbow, Soarin who's obviously didn't know about his own argument with Fleetfoot and Fleetfoot herself

The food weren't eaten, probably because Rarity just want to keep her image of thin and slender

That's my theory, I could still be wrong of course.

4719009 Yeah, I've read too many mystery novels, so I might be seeing shadows where they aren't and might be way off base, but I think one of those ideas will stick to the wall come the end of story.

Plus, if I'm right, then I have Reeve's permission to feel slightly chuffed about myself for a time. And I so want to feel chuffed!

Ok, I know it's a bit too late, but I know who the mastermind is! I had my suspicions during last trial, but here it's finally been confirmed: the mastermind is Trixie!

I mean, think about it! It's wierd that the current mastermind knows exactly, word for word, what Twilight said during the first trial about having sixteen spots at the trial. It should also be noted that Trixie had a thing for Twilight, so it doesn't seem that far-fetched, right?

Anyways, I need to finish this fic to find out....and I'm invested every step of the way!