He might still be alive if he didn't roll down the window. He didn't know if a word or the barrel of a gun was going to come out.
Might have made a big difference as well if the words that were to come out of the window were in English.
I don't buy the GF's story, either. If he was backing out, meaning the vehicle was in motion AND gear, shooting the driver in the head would make for a very "interesting" ride.
Also, if he was using a GPS, he had to know the correct address. If you pull into someone's driveway, and the number on the house isn't the one one you are looking for, why do you wait for the owner to come out?
Dressing like a human being, and not some hoodrat, goes a long way as well.