I'm having a hard time swallowing all of the comments regarding the design of the Glock, with references to the fact that an added safety may have prevented this "accident." What? Are all of these people now proponents of the "protect the people from themselves" line of thought.
The way things look to me, this may very well have happened even if the firearm had a grip safety. The guy was carrying in improperly, in an overly worn holster and had it in his waist band in a manner that would have him sitting on it. How many safeties are required to render a handgun safe? Or, how safe does a handgun have to be to protect a guy from himself?
As far as I see it, there was no malfunction. As far as I see, it was just a matter of time before this sort of incident occurred. A set of circumstances were created that could have lead to no other outcome, and was going to happen sooner or later. All a grip and/or thumb safety would have done was to add a false sense of security.
I've always been taught and have read many times on this forum that you should NEVER rely on a mechanical safety anyway.
I'll say that if the OP had been carrying his Glock in a proper molded holster, this would never have happend either.
As for carrying in condition 3, to me that's just carrying around an empty firearm.