Sanhedrin 79A

והיה בה כדי להמית על לבו, והלכה לה על מתניו, ולא היה בה כדי להמית על מתניו, ומת ⁠– פטור.

and the blow was powerful enough to kill him were it to land on his chest over his heart, and instead the blow landed on his loins, and it was not powerful enough to kill him when it landed on his loins, and nevertheless the victim died, the assailant is exempt. Although the assailant intended to kill the victim, the blow was not powerful enough to kill. Ostensibly, his death was not a result of the blow.

נתכוון להכות את הגדול, ולא היה בה כדי להמית הגדול, והלכה לה על הקטן, והיה בה כדי להמית את הקטן, ומת ⁠– פטור. נתכון להכות את הקטן, והיה בה כדי להמית את הקטן, והלכה לה על הגדול, ולא היה בה כדי להמית את הגדול, ומת ⁠– פטור.

If one intended to kill an adult and the blow was not powerful enough to kill the adult, and instead the blow landed on a minor, and the blow was powerful enough to kill the minor and the minor died, the assailant is exempt. If one intended to kill a minor and the blow was powerful enough to kill a minor, and the blow landed on an adult and the blow was not powerful enough to kill the adult, and nevertheless, the adult died, the assailant is exempt.

אבל נתכוון להכות על מתניו, והיה בה כדי להמית על מתניו, והלכה לה על לבו, ומת ⁠– חייב. נתכוון להכות את הגדול, והיה בה כדי להמית את הגדול, והלכה לה על הקטן, ומת ⁠– חייב. רבי שמעון אומר: אפילו נתכוון להרוג את זה והרג את זה ⁠– פטור.

But if one intended to strike another on his loins, and the blow was powerful enough to kill him were it to land on his loins, and instead the blow landed on his chest over his heart, and he died, the assailant is liable, since in any event, his intent was to kill the victim and the blow was powerful enough to kill him wherever it struck him. If one intended to strike an adult and the blow was powerful enough to kill the adult, and the blow landed on a minor and he died, the assailant is liable. R' Shimon says: Even if one intended to kill this one and he killed that one, although he would be liable for killing either, he is exempt, because one is executed only if his action completely corresponded with his intent.