Stakeout At Public Toilet 7W2

The nurse came out of the public restroom at 7W2. Twenty feet away partially hidden behind an opaque partition was me, scrutinizing her and not particularly hiding that.

"Why are you using that restroom?" I asked suspiciously. I was suspicious because I knew she worked on 6. 

"You work on 6. Why did you come up to 7 to use my restroom?" I think I said "my." I might have said "the."

"The toilets on 6 are naaaaasty," she said, "Why? Was that one closed?"

Deducing that this was not the culprit I was trying to catch on my stakeout, I apologized slightly for my rudeness and explained that for the last 20-25 days someone.....someone I'm trying to catch....has been poopifying 7W2 in a manner that cannot be accidental or gastronomical or a product of powerful hospital medication. Someone has been doing evil to my 7W2 toilet and I intend to catch them.

A few hours later I saw that same nurse down in the smoking area talking with one of the other janitors. Seeing me walk in, she said, "I will never use that toilet again." 

The other hospital housekeeper looked at me strangely with a mixture of curiosity and admiration. We housekeepers prefer that the other hospital employees not use the public restrooms but rather the ones designated for staff. That way we can narrow our list of suspects.