Haha, nice work dude.
I had a flatmate that I kicked out recently that kept getting into my booze cupboard.
At first I thought the same thing as you,( Couldnt remember drinking it but maybe I did
)
After a few weeks though I noticed that a completely full bottle of vodka had gone missing, asked aroung the flat, no-one knew anything... hrm.. was I going mad?
Then I noticed all sorts of other bottles near empty so I marked each bottle level with a pen and left it for a few days.
Sure enough 3 bottles had emptied almost 1/4 in that time and I knew which flatmate it was because the other one was away.
Showdown time with the flatmate and she swore that she didnt touch it which I wasn't buying so I kept pushing and she admitted that " Maybe I drunk it, I cant remember" huh?!?
This uncovered an drinking problem and being semi kind hearted I offered help and opted not to kick her out.
Bad Idea.
Some nights she would sneak in and you'd hear a loud thump late at night, she'd be passed out in front of the heater and I'd have to get up and move her so she didnt catch fire.
It got worse, mistrust formed and eventually she would attempt to fill the bottles up with water again to hide it (Trying to disguise it by filling up red wine bottles with water probably wasnt one of her most masterful plans, neither were bottles that were 1/2 empty ending up almost full)
Things just got too awkward, safety of others became an issue so she got the ole boot and we called her family to try and help her out.