Trap them. Use glue traps baited with peanut butter. The animal might get away, but there will be enough fur left for you to identify it.
I can’t get up there myself. There is no stair that folds down. There is just a square opening in the hall ceiling, with a piece of painted plywood resting in the opening. To get up there, you need a full sized ladder, which I don’t have. I asked my very large, karate instructor neighbor to go up there and check it out, but he was afraid to do it! He helped me toss the bags of mothballs up there, but he would only move the plywood an inch or so to admit his hand before tossing the bag.
There are people who know how to trap the beasts (without killing them). We had racoons in our attic once. They came used cage traps. Racoons love marshmallows, and that’s what they baited the traps with. It worked, they took them away to some wooded place and turned them loose.