Found this on the web. Don't know if it's of any use in finding the imposter!
the smell of marijuana is itself the olfaction of pure chemicals, specifically terpenes (beta-caryophyllene). This is how police canine trainers teach their dogs to identify the smell. But these terpenes are quite common. There are more than 200 terpenoids in marijuana alone, but many other non-marijuana sources of terpenes are just as common.
The most common terpenoids include limonene, myrcene, alpha-pinene, linalool, beta-caryophyllene, caryophyllene oxide, nerolidol, phytol, and often do not even come from the marijuana plant itself (while giving off similar scents). As a result, many things with these terpenoids, such as skunk scent, marigolds, skunk cabbage, hops, and even various combinations of rotting garbage can create nearly identical smells.
