The filing cabinet mouse

Yep, there's a mouse in one of my filing cabinets at work.

I first noticed evidence of him about a week ago.  I had left a packet of crackers in my "personal" drawer, and something had chewed through the plastic and eaten part of a cracker. 

Bemused, I put some of the dry cereal I keep at work to snack on in the drawer.  The next day it was gone, and he had thoughtfully left behind some mouse poop pellets.

Next, I put some dry cat food in there.  Gone.  Apple slices?  Check.

At this point I figured that he probably could use a more balanced diet, so I picked up some hamster/gerbil food.  He likes it! Or, well, he eats it, anyway.  He also ate a green bean and a carrot slice from my lunch soup the other day.

Now, I am just guessing that this is a mouse, judging by what he leaves behind.  I've never actually seen him.  And I can't for the life of me figure out how he's getting into and out of a metal filing cabinet, but then again I can't access the back of the cabinet because it's built into my work area.  Maybe the back of it is open?  I dunno.

But I DO know that my cats would laugh me out of the family if they knew I was harboring a mouse in my filing cabinet.