If you have access to the attic, you should place a Have A Hart trap or equivelent in the attic. You might be able to borrow one from your Animal Control Officer or if you have to, you can buy one at Home Depot.
Poison works but, you really don't want it die in your walls. Besides, with a Have A Hart, you know when you have caught him.
Do not close the hole up with the critter in the house!