The thing that confuses me is the furniture placement, it's definitely not a bookcase in the first photo, there is a stain clearly visible on the floor in a crescent like shape. When you see the image with the key you will note that the bookcase is placed over it, which makes its proximity to the door in the second photo easier to understand.

I was searching for the plug and wire in the first image and couldn't see it in relation to the desk. Clearly the bookcase has been moved, but these photos were, I believe, taken on different dates - note the sheet on the mattress in this later imagehttp://www.stevenaverycase.org/wp-content/uploads/2016/01/exhibit-Avery-bedroom.jpg that correlates to the position of the bookcase when the key was found.

(If the first image was taken after the key find, the slippers would not be where they are because they were taken into evidence)

I am not suggesting that the investigators moved the furniture, perhaps they did but I can't see the motive for it. However, even if SA moved the furniture from elsewhere in his home into his bedroom, or even from elsewhere in the bedroom, the key would surely have fallen out then, the 'vigorous' shaking that they claimed to have given the bookcase yet still allowed items to remain in it, can't have been anymore disruptive to it's contents than moving the bookcase from a prior location.

Or perhaps he even emptied the contents of the bookcase when he moved it from A to B - anyone finding a key they know would connect them to a crime they committed would destroy it. Or maybe the bookcase was a recent addition to SA's furniture - are there photos of it located elsewhere in his home from the first search?