|Reb Chaim Soloveitchik Zt"L|
מאי חזית דדמא דידך סומק טפי
R. Chaim Brisker* says It is a Gezeiras Hakasuv to kill a Rodef, in order to save the life of the Nirdaf. If not for the Gezeiras Hakasuv, we would not have been allowed to kill the Rodef. We may not kill one person to save another persons life.