I had squirrels get in between the drywall in my old house. Had a professional take out the first one...he cut a hole in the wall...
The second one, I just let die...it stunk for about a week. But I didn't have a hole in the wall.
Somehow they could get into the attic, but we never could figure out why.
I've had two squirrels get into this one. First one, the cats chased into the bathroom....
when I was in there going potty.....ok that was a shock. We got that one trapped in a corner in our bedroom, and released it out into the yard.
The second one the cats chased up here into my office, and I knew it was in the house when it went running past me ... I was laying on my loveseat reading a book....and the cats jumped over me to get to it. They chased it back downstairs to our room where we caught it in the bathroom. We released that one out front too.
Both were fairly young, and we have a very small unscreened gap on the porch between the stone and the door frame and we think they came in that way, because we keep the door from the family room to the porch open just enough for the cats to go in and out as long as it's about 55 or higher outside.