Peanut butter on a simple snap trap will tell you if there are mice in there. If they are getting away, “glue” a chocolate chip to the trip mechanism with Karo syrup. The mouse will have to work at it and even the sneakiest mouse will be caught.
I maintain bait stations all over the farm and around the house. Never had a mouse die inside something. I’ve heard they seek water when the poison takes effect which causes them to go outdoors. I have no idea if this is true or not, but since the poisons cause internal bleeding it would seem reasonable.