While stationed in Germany many years ago, we lived in base housing apartments which consisted of three floors and a common basement. If I could remember correctly, there were 12 units, thus 12 families in each building. My daughter’s two hamsters got loose, and were in the walls.
I had to alert the 11 other families that if they see little rodents in their quarters, it might be our hamsters and not mice. We never did recover them!
Did you ask the cat?