do not let him go free from punishment

"be sure to punish him"

bring his gray head down to the grave with blood

Blood is a metonym for violent death, and the head is synecdoche for the whole person. Alternate translation: "make sure he dies a violent death" (See: rc://en/ta/man/translate/figs-metonymy and rc://en/ta/man/translate/figs-synecdoche)