Reference for Sanhedrin 90:12

וליגמר מיניה משום דהוה רוצח וגואל הדם שני כתובין הבאין כאחד וכל שני כתובין הבאין כאחד אין מלמדין

But where it is not possible to execute him in the manner prescribed,<span class="x" onmousemove="('comment',' E.g., if he fled, but could be reached by an arrow (Rashi on 72b). ');">²²</span> whence do I know that one may execute him by any means possible? From the verse: He that smote him shall surely be put to death, — in all cases'?<span class="x" onmousemove="('comment',' Infra 53a; 72b. Hence it is not necessary to understand the verse literally. ');">²³</span>

Jastrow