I think so (it's been quite a few years since my brief foray into law school). Let me do some quick Googling...

Yep, there it is: Looks like it may vary in different jurisdictions, but

a defendant’s right of self-defense "transfers" (just as intent to kill does) from the intended to the actual victim...If the defendant, acting justifiably in self-defense against an aggressor, fires a weapon "wildly or carelessly," thereby jeopardizing the safety of known bystanders, some courts hold the defendant guilty of manslaughter (or of reckless endangerment if no bystander is killed), but not of intentional homicide.

FWIW, "You have to want someone dead, not necessarily the same person" is essentially how "intent to kill" works in a legal sense. That is, the distinction between murder and manslaughter is whether, by your actions, you intended to kill someone; under the law, it doesn't matter whether the person actually killed was the person you intended to kill, or not.

Not that the rules of magic are necessarily modeled after modern US jurisprudence, but it might be that they both reflect a deeper moral concept.