I'm thinking it was a flatbed. No glass and I'm positive I can hear my truck on start-up.
Of course my security cam system has a bad HD so I have zero footage, I hate thieves more than anything and this experience is very frustrating, but On-Star has been great. And no, the truck is not phoning home to On-Star, which leads me them to believe the battery has been disconnected.
All this tech (sans a battery back-up device) and they still get jacked. really amazing.