I saw a mouse in my unfinished basement on 11/30 evening (just moved into this house in Spring) and noticed that it was happily living off a bag of sunflower seeds. I removed the sunflower seeds immediately , set up a trap and on 12/01 morning threw out the dead mouse. And while I was doing that, I spotted another mouse that scurried away!

My unfinished basement only has cardboard boxes, my son's toys and sunflower seeds was the only food item. I found the nest inside a pile of heavy curtains... no babies or anything, just a gathering of sunflower seeds. I threw the curtains out as well. I set 4 traps [bait: raisin dipped in peanut butter] for it on 12/01 but the trap didn't catch any when I checked this morning on 12/02.

But now I am scared. If the mouse is not in the basement, where could it be? Please don't tell me it has moved upstairs (upper two floors) from the basement because I took away its food source and threw out the nest.

1. Should I set traps on my upper two floors as well? If yes, where should I place them?
2. Do I need to call an exterminator? Can they confirm and declare a house mouse-free?
3. What materials other than concrete can I use to seal the entry point in the ground/mud? And where do I buy it? I saw a hole under the tile leading to my walkout basement.
4. Is it possible the mouse left the way it came in?