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?
The decision is not about what the agent did, it is about holding the government responsible for the agents actions. The agent is the one who committed the offense, not the government.