On November 2005 the Wisconsin State Crime Lab entered the garage and sprayed it with luminol, a substance which emits a bluish glow when it comes in contact with blood. After the spraying had been done, all doors and windows were closed and lights were turned off to make the garage completely dark. Behind a lawnmower a 4'x3' spot emitted a faint bluish glow.
In May 2006 Brendan Dassey made several drawings of the crime scenes, including one of the garage. He drew an almost empty garage, with only a snow mobile and a lawnmower inside it. Right behind the lawnmower he drew the victim lying on the floor and between the lawnmower and the victim he drew her blood. The exact same location where the luminol had lit up. Brendan described the blood as 4'x3' in size.
At trial Brendan explained that on the night of Halloween, several hours after the victim was on the property, he and his uncle cleaned one spill in the garage, while they were having a bonfire outside. The spill was cleaned with gasoline, paint thinner and bleach.