If your bullet traveled through the intended target, it did not go astray. The fact that it went through one body to hit someone else is ... I don’t know. If someone is killed as the result of someone else’s criminal assault, wouldn’t the instigator be charged?
In many states the law labels any death that clearly results from the commission of a felony as “Felony Murder.” Where Felony Murder falls in the criminal code varies from state to state. In New York it is classified as a form of Second Degree Murder. In Texas it can be prosecuted as Capital Murder.
I do - you're still liable. Anyone but a cop would have his choice in ammo critically examined, and he'd be sued over it, and lose. Cops are actually allowed extra- powerful loads, which undoubtedly contributed to the ability of the bullet to travel completely through one person and then kill someone else. If you used such a load and did the same thing, you'd be toast for it.
These rules are widely known. I grew up with them. Note #4
The Four Rules
1. All guns are always loaded. (Treat them so!)
2. Never point the gun at anything you are not willing to destroy.
3. Keep your finger off the trigger until your sights are on target (and you have made the decision to shoot).
4. Be sure of your target and what is beyond it.