Yeah. The number of people who actually had access to poison looks like it's restricted to
1. People with a role that could make them start with poison.
2. People who could steal the poison from those people who started with it.
3. People who visited the school store at one point in time.
List of Roles:
SSBM (Super High School Level Super Spy)
Dexter28 (Super High School Level ????)
Ushiromiya Kamikaze (Super High School Level Vanilla)
Solfadore (Super High School Level Inflatable Boat Master)
Eternal Rival (KCF) (Super High School Level ????)
shadosneko (Super High School Level ????)
Tom (Super High School Level ????)
Regaro (Super High School Level Lion Tamer)
Kanz (Super High School Level Runner)
Ryoko (Super High School Level Fat Girl)
Sceptile (Super High School Level ????)
Silverline182V (Super High School Level Alchemist)
saveus_Maria (Super High School Level CSI)
Biscuit (Super High School Level Wrestler)
JC (Super High School Level Surfer)
Spiral (Super High School Level Journalist)
Those are all the 100% confirmed roles, I believe. This leaves out the Psychic, the Spy, the Zombie, the Avenger, and the Fat Girl (which we know Ryoko is but she may or may not also be something else at the same time). It also assumes that Lisel isn't lying to us. If he is, we're in trouble.
I'm curious about the Avenger role. It's the vaguest of the bunch.
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Black Turtle did a pretty good job.