LAST EDITED ON 07-08-13 AT 01:34 PM (EST)
You can get Benzene (the petroleum naptha version) in chemical supply stores. Or you used to be able to, I don't think it has ever been a restricted chemical.
I think Geno did it. He seems to be generally backgrounding it, with his main contributions to be in the way of leading others astray. Offhand, I don't recall when he's ever advanced the sleuthing. Additionally, there is his professed profession, "Bar Trivia Host". That just has to be an invention, right?
The woman that was "scared" along with Don (this time) is my second leading suspect, with the lack of clues she had this time she should have been the more clueless (heh), so her not being booted is suspicious, and her repeated "scared cards" might be an attempt to throw us off her scent.
This has turned out to be more a game of social skills, not so much a game of deductive skills. And they have some social ninnys.