Parashas Masei · Passuk 35:31 · TT note 3
Chabad.org — English translation + Rashi
Torah Temimah points to Sifrei (TT note on “רָשָׁע לָמוּת”).
English: Therefore one who is going out to be executed after his verdict has been completed, and others wounded him or killed him — they are exempt.
Once the capital verdict is final, intervening harm or killing by others incurs no liability.
A person already sentenced to death is treated as legally “dead”; subsequent injury or killing by third parties is not actionable.