Rear window defroster overheated/caught on fire. It will be available for inspection unless GM rectifies the issue and removes the components in question. Cabin filled with smoke and a small fire broke out immediately behind the rear headrest/seatbelt location. Rear window section shattered, most of the glass is intact but some pieces were ejected. The problem has been reported to GM but is still in the investigation phase. The vehicle has not yet been inspected as I have just started the report filing with GM. No warnings, indicator lights, etc. were present before, during, or after the incident.