The Bookcases were about 350mm to wide for the space I was filling so I cut them down to size. I also wanted one of the units to be suitable for holding CDs so I added some extra shelves on one of the bookcases using leftovers from the other two.
I am not going to show all the assembly steps. The key thing here is shortening the thick outside frame of the bookcase.
Basically I had this
Step 1: Goal
And I wanted shelves halfway each section as well
I assembled the thing first to mark where I wanted to cut.