Evidence against Poppy and Egon
I've done some focused reading, looking at just these two characters and the death scenes.
Poppy:
"Now let's clean you up" in scene 2 (she carries wet ones in her satchel)
Mentions of flowers: The flower pin in scene 3 and pushing up daisies in scene 4
Potions: Particular expertise with potions and ingredients in scene 3
She is a marvelous cook, and there is that odd ending to scene 4 with the hungry giant.
Someone protested that the mafia didn't cook, but they were cooking up a potion in scene 3.
It's possible she has the most cluttered satchel (getting back to the disoranization note from Malfoy). Along these lines, she is not into "abstract" magic, and the fourth scene talked about them not using magic. But these are a bit weaker.
Egon: In addition to the other reasons people voted for him, the fourth killing utilized 2 wands. Sure they were from different students. Saying one student provided both wands would be a little unsubtle.
Well, since I am more sure Poppy is mafia, I think I have a pretty high probability of getting hit. Which would be just since I lead off the voting against the doctor. But I hope I am around tomorrow. Ta ta for now.
Got my eye on you...