Numbers 35:19

35:19 The avenger of blood himself must kill the murderer; when he meets him, he must kill him.

Numbers 35:27

35:27 and the avenger of blood finds him outside the borders of the town of refuge, and the avenger of blood kills the slayer, he will not be guilty of blood,

tn The participle גֹּאֵל (goel) is the one who protects the family by seeking vengeance for a crime. This is the same verb used for levirate marriages and other related customs.