After they find the room in the house where Amy lost all her blood they smell bleach, which indicates that someone cleaned the room. They use Luminol to find the blood stains on the floor and walls. But if someone uses bleach to clean up blood, you would see smears from where they cleaned as Luminol reacts with bleach as well. But the Luminol shows no such smears, just the original blood stains. This would indicate that no cleaning was done.