Ours often brings fieldmice in, alive, and lets them go. Last week, he brought one in and let it go in the bedroom, which we are decorating. Next day, I picked up a dustsheet from the floor, the mouse legged into a corner and four babies dropped out of the dust sheet!! I made them a nest in a tissue box with a hole in the side for Mum to get access, we baited a humane trap with peanut butter, and waited, and waited. I expected the pups to be dead the next day, but no, she must have been feeding them. It took FIVE days before she had eaten enough peanut butter to make her trip the trap. She and the babies were then reunited in a suitable spot outdoors, with a piece of wood over the nest" to make sure they didn't get wet! Happy ending!