Still don’t know why you couldn’t just turn off the key...
I think he cracked and committed suicide.
I'm not a hacker but I suspect the key turn-off could be overriden. For example, in my truck with the key turned off, the windows and be rolled up and down, the radio still works, etc. UNTIL I lift the door handle. Then everything goes dead.
If the Benz had the equivalent of OnStar, that could provide access via wireless. We've all heard the OnStar commercials where the doors are unlocked via a wireless command.
Up thread there was some speculation about how the hacker could steer the car. The hacker doesn't need to. Kill the brakes. Turn off the airbag. Invoke maximum acceleration. Who cares where the car goes? The driver is dead on impact with almost anything.
IMHO, doing this wirelessly is the hard way. Much easier to hack the computer to react to some event such as going over x miles per hour. The hack could have been done while the car was in a parking lot or garage.