As it's been confirmed already, I drank red wine that night. I don't stop by the bar too often, twice or thrice a week at most. It's a convenient place to find company at a late hour, and we were a good number on Wednesday night.

Poisoning is the easy part, frankly. Anyone could've slipped poison inside specific bottles earlier, anytime during Wednesday. The killer just needs to know when the victims retire, they could keep watch anywhere between the bar and the bedroom wings, as long as it allows them to beat witness. The bar's the simplest place, but they could divert suspicion away from themselves by not being present during the evening. It's not too hard to bump into someone living on the upper floors by the main staircase while they're headed to bed, after all.

[a beat.]

Then there's the speed of the poison, if we can determine what was used and how long it needs to take effect.