I do not think the owner can be. The person who left the gun there was the party whose actions resulted in a gun being stolen, then used to kill Kate Steinle. Let's apply the same principle in another scenario:
What if the car was a rented car? Would the car rental agency be responsible for the actions of the renter? I would vote no on that question.
To me, this seems like an example of going after deep pockets. Don't get me wrong, her death was a terrible tragedy, and the man who killed her should rot the rest of his life in jail.
As to the guy who left the gun in the car, he is the one who should have been sued (maybe he was?).
When it comes to courts and case law logic is out the window
You are ignoring the laws of tge state wherein the killing took place. It is unlawful to what the VLM agent did. That alone makes the ligic trail different.
If you left your car running and unlocked, and a kid hopped in and ran over little suzy, you’d be in the suit as well as likely facing criminal charges....
No?
Loaded gun in non locking container in the open in a sedan in a public lot? What’s the problem?