Spoiler here. The husband was guilty. How am I so sure? Easy. The fireplace. The husband was obsessed with keeping the house cold. If there's a body in the attic, he would have to keep it cold. He's outraged when the cop puts too much wood on the fire to raise the temperature of the house. Then the cadaver dog alerts from the driveway. He then "discovers" the body in the location he had hidden it from the police with incorrect floor plans. Inept police? Definitely.