The question I need answered, which I cannot find an answer to, is:
Someone in a basement room, no windows, has died by ingesting cyanide. (It was in a glass vial which was cracked open, so the poison was exposed to the air before being ingested.) The body has since been removed from the room. Would there be any tell-tale smell remaining in the room? The time scale here is somewhere between 1-6 hours after the death. (The body was discovered and removed almost immediately afterwards, but the character does not go into the room right away.)
In the course of my Googling I found a site which mentioned that cyanide evaporates and disperses quickly, but given that this is a room with almost no air flow, I didn't want to extrapolate.