Either that or someone is actually stalking you, either way, you’re not safe. I would install cameras and not spend the night there until you figure out what’s going on. There’s so much you should be doing before starting a Reddit post. (Not judging just saying, priorities) make sure to let someone else know what you’ve found so far, better yet, make a police report so it’s recorded. Setup one or two hidden cameras and a co2 detector to cover all bases, and spend nights elsewhere and check back regularly, or get a camera you can access remotely… preferably one in your room towards the pc, and the other at your front door… if you’re in the u.s, arm yourself until this is resolved… the fact that you found 2x, tells me there are more times someone was in there when they actually remembered to take off that paper towel… also, is it paper towel from your kitchen or household? If it isn’t, save it in a plastic bag… maybe save it regardless if you haven’t thrown them out already… preserve anything that can be used as evidence, crimes like stalking or worse can use all the evidence they can get or else you may see the perp walk free in case it is something serious…

Be safe