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Bravo, Rune, Nightwolf, and totalinfinity! You guys got the solution!
The story begins with Ethan's health. His health was pretty bad; in fact, he was dying. He had only a few more months to live. That's when he decided to play one last practical joke on his old friends and prove to them once and for all that he was smarter than they ever would be. To him, suicide was preferable than dying in some hospital bed.
He dismissed all of his servants for the weekend and made the necessary preparations. After his guests arrived, the day proceeded as a normal until that night. After all the guests had fallen asleep, Ethan went upstairs (via elevator) and started planting evidence. He stole a bathrobe belt from Emily's room, planted a gun in Rick's room, and lifted some fingerprints from Manuel's room. None of the guests had heard anything, because all three of them had been drugged during their dinner and had fallen asleep shortly after going into their rooms.
Next, Ethan made a noose from the belt and attached the end to one of the upward-going cables through the grate on the elevator ceiling. He then carefully applied Manuel's fingerprints to the elevator buttons, and ever so gently...pushed the down button. The noose tightened, his neck broke, and eventually the belt tore and slipped up and out through the grate, leaving only a single fiber on Ethan's body where it would be found the next morning.
It would be the last practical joke that Ethan ever pulled on his friends. Don't think too harshly of him, though. Remember that he made all of them beneficiaries in his will. He felt bad for all the troubles he caused for his old friends, so he left his entire fortune and detective agency for them to share together. So...
First case: solved!
Now it's someone else's turn to post an interesting case.