One of my roommates smokes indoors

So one day when i was in my room I smelled something that smelled like it was burning. Stepped out of my room to ask my roommates if something was burning.

He responded "No. We're smoking."

Then I just said "Okay."

I don't smoke anything at all. Never have and never will. But I am pretty sure that my roommate was smoking weed in the house.

I personally don't smoke anything. And I usually mind my own business if I find out about my friends or coworkers smoking anything. But when you smoke INDOORS it seems worse. Not only is it a fire hazard, but it also smells bad and the scent could possibly get stuck in the vents and on the carpet and furniture.

If I complain to my landlord about it then my roommate will easily figure out that it was me who spoke about it.