I blame both unless the criminal steals it from a secure lock box in the car. The criminal should not be stealing and the gun owner should no better. Personally if I leave a gun in my car and it is stolen, I am going to be kicking myself for being stupid.The fifth rule of gun safety should be to keep guns secure from unauthorized access.
We generally agree that the traditional 4 rules of firearms safety are there to protect life and property.
But, nobody here wants to be told that they are expected to be responsible when their 2A rights or property is concerned.
Blaming criminals for stolen guns is a red herring.