The removable back panel is retained by two tool-less thumbscrews at the top.
These are very similar to the originals
https://www.mcmaster.com/1626A42/ (https://www.mcmaster.com/1626A42/)
Adjustable-Tension Tight-Hold Cam Latch
with Knob, Zinc-Plated Steel, 1/16" to 1/4" Latching Distance