This step can get a bit messy! There is a second glass sheet glued to the back that I believe acts as a capacitive plate. I don't know the exact specs for the adhesive spacer used, but the way it smells, I would guess it is a cyanoacrylate derivative and would produce toxic fumes when heated. So it must come off!

start by removing the wires and the button and the camera fixture.

Fortunately the second sheet has similar properties to sugar glass, so it breaks into small pieces quite easily. Be sure to wear eye protection as the needle-sharp pieces fly everywhere. Don't use any solvent at this stage as the glue will help keep the glass shards bound when they shatter.