It was taught: Rabbi Yonatan says, a pursuer who was chasing after his fellow to kill him, and the rescuer could have saved the victim by maiming one of the pursuer's limbs yet did not, but killed him, is himself liable for the pursuer's death, as it is written, "And if men strive together" (Exodus 21:22). And Rabbi Elazar said the verse speaks of a quarrel involving danger to life, and it is written, "And if harm follows, you shall give a life for a life." Yet even so the Merciful One said, "And if no harm follows... he shall surely be fined." Granted, if you say that when one could save the victim by maiming a limb he is not permitted to save him by killing the pursuer, then you find a case where he is fined, namely where he could have saved by maiming a limb. But if you say that even when he could save by maiming a limb he may also save by killing, why should he be fined? Granted, according to the Rabbis who say that one who intended to kill this man and killed that man is liable, this fits what is written, "And if men strive together," which Rabbi Elazar said speaks of a quarrel involving danger to life, as it is written, "And if harm follows, you shall give a life for a life." But according to Rabbi Shimon, what does he do with it? He needs it for monetary payment, in accordance with Rabbi, "you shall give a life for a life" meaning money. Rav Acha said: the teaching of the school of Chizkiyah departs from both Rabbi and the Rabbis, for the school of Chizkiyah taught "one who strikes a man" and "one who strikes a beast" (compare Leviticus 24:21): just as with one who strikes a beast you drew no distinction, and so on. What is meant by "who does not intend"? If we say one who does not intend at all, that is simply an accident. Rather, one who does not intend to strike this one but another; and it teaches, not to make him liable for money but to exempt him from money, for if he were subject to death, why would he need to be exempted from money? Rather, learn from this that he is neither subject to death nor subject to monetary payment.
The Pursuer Who Could Have Been Stopped by a Lesser Blow
Yalkut Shimoni on Torah 335:5
תַּנְיָא, רַבִּי יוֹנָתָן אוֹמֵר, רוֹדֵף שֶׁהָיָה רוֹדֵף אַחַר (אָבִיו) [חֲבֵרוֹ] לְהָרְגוֹ, וְיָכוֹל לְהַצִּילוֹ בְּאֶחָד מֵאֵבָרָיו וְלֹא הִצִּיל, נֶהֱרַג עָלָיו, דִּכְתִיב וְכִי יִנָּצוּ אֲנָשִׁים, וַאֲמַר רַבִּי אֶלְעָזָר בְּמַצּוּת שֶׁבְּמִיתָה הַכָּתוּב מְדַבֵּר, וּכְתִיב וְאִם אָסוֹן יִהְיֶה וְנָתַתָּה נֶפֶשׁ תַּחַת נָפֶשׁ, וַאֲפִלּוּ הָכֵי אֲמַר רַחֲמָנָא וְלֹא יִהְיֶה אָסוֹן עָנוֹשׁ יֵעָנֵשׁ, אִי אֲמַרְתְּ בִּשְׁלָמָא יָכוֹל לְהַצִּיל בְּאֶחָד מֵאֵבָרָיו לֹא נִתָּן לְהַצִּילוֹ בְּנַפְשׁוֹ, הַיְינוּ דְּמַשְׁכַּחַת לָהּ דְּיֵעָנֵשׁ, כְּגוֹן דְּיָכוֹל לְהַצִּיל בְּאֶחָד מֵאֵבָרָיו, אֶלָּא אִי אֲמַרְתְּ יָכוֹל לְהַצִּילוֹ בְּאֶחָד מֵאֵבָרָיו נַמֵּי נִתָּן לְהַצִּילוֹ בְּנַפְשׁוֹ, אַמַאי יֵעָנֵשׁ. בִּשְׁלָמָא לְרַבָּנָן דְּאַמְרֵי נִתְכַּוֵּן לַהֲרֹג אֶת זֶה וְהָרַג אֶת זֶה חַיָּב, הַיְינוּ דִּכְתִיב וְכִי יִנָּצוּ אֲנָשִׁים וְאָמַר רַבִּי אֶלְעָזָר בְּמַצּוּת שֶׁבְּמִיתָה הַכָּתוּב מְדַבֵּר, דִּכְתִיב וְאִם אָסוֹן יִהְיֶה וְנָתַתָּה נֶפֶשׁ תַּחַת נָפֶשׁ, אֶלָּא לְרַבִּי שִׁמְעוֹן מַאי עָבִיד לֵיהּ. מִבַּעְיָא לֵיהּ לְמָמוֹן, כִּדְרַבִּי, וְנָתַתָּה נֶפֶשׁ [תַּחַת נָפֶשׁ], מָמוֹן. אֲמַר רַב אָחָא, הָא דְּתָנָא דְּבֵי חִזְקִיָּה מַפְקָא מִדְּרַבִּי וּמִדְּרַבָּנָן, דְּתָנָא דְּבֵי חִזְקִיָּה (ראה ויקרא כד, כא) "מַכֵּה אָדָם", "וּמַכֵּה בְהֵמָה", מַה מַּכֵּה בְהֵמָה לֹא חָלַקְתָּ בּוֹ וְכוּ', מַאי שֶׁאֵינוֹ מִתְכַּוֵּן, אִילֵימָא שֶׁאֵינוֹ מִתְכַּוֵּן כְּלָל, הַיְינוּ שׁוֹגֵג, אֶלָּא שֶׁאֵינוֹ מִתְכַּוֵּן לְזֶה [אֶלָּא לְזֶה], וְקָתָנִי לְחַיְּבוֹ מָמוֹן אֶלָּא לְפוֹטְרוֹ מָמוֹן, וְאִי בַּר קְטָלָא הוּא לְמַאי אִצְטְרִיךְ לְמִיפְטְרֵיהּ מָמוֹנָא, אֶלָּא, לָאו שְׁמַע מִינָּהּ לָאו בַּר קְטָלָא הוּא וְלָאו בַּר מָמוֹנָא הוּא.