A person who is authorized by law, or who is duty-bound, to kill a murderer is called go'el ha-dam – usually translated as an avenger of blood, but more accurately to be rendered as a redeemer of blood (cf. Lev. 25:25; Ruth 3:12; I Kings 16:11).
The avenger's rights were further restricted by being made subject to and dependent on the prior judicial conviction of the murderer – whether the murder was premeditated or not was a question not for the avenger but for the court to decide (Maim. loc. cit. 1:5, following Num. 35:12; "the manslayer may not die unless he has stood trial before the assembly"; but cf. Yad, loc. cit. 5:7–10). Opinions of later jurists were divided as to what the avenger's real function was; some held that he initiated the proceedings, searching for the murderer and bringing him to court for trial (Ramban; Nov.; Sanh. 45b; Beit ha-Beḥirah ad loc.); some thought he should appear before the court and participate in the proceedings as a prosecutor (Nissim Gerondi, basing himself on the Targum pseudo-Jonathan who renders go'el ha-dam as "claimant of blood"); others relegated the avenger to the role of an executioner, it being his right and privilege to execute the death penalty pronounced by the court (Yad, loc. cit. 1:2; Ritba, Nov., Mak. 10b). That the avenger had a locus standi in court appears probable from the scriptural injunction that the court "shall decide between the slayer and the blood-avenger" (Num. 35:24). While the slayer would protest his innocence or, alternatively, his lack of malice, the avenger would plead premeditation (cf. Malbim ad loc.); by finding a lack of malice, the court is said to "protect the manslayer from the blood-avenger" (Num. 35:25). When an alleged murderer stood trial but was not convicted (either because of lack of sufficient evidence or because the verdict had not yet been given) and the avenger killed him, most jurists held that while the killing was unlawful, the avenger was not guilty of murder (Beit ha-Beḥirah, Sanh. 45b) – the proffered reason being that the avenger had a better right to kill than even the unintentional manslayer (Yad, loc. cit. 6:5), or that Scripture itself recognized the avenger's "hot anger" (Deut. 19:6) as negating premeditation (Redak to II Sam. 14:7). However, if the avenger killed the murderer within the walls of the city of refuge, it was murder pure and simple (Tosef., Mak. 3:6).
Any next of kin entitled to inherit the deceased's estate qualified as an avenger (Yad, loc. cit. 1:2). Some later authorities even include maternal relatives although they are not in line for inheritance (Or Same'ah to Yad, loc. cit., against Maimonides). Women also qualify as avengers (Yad, loc. cit. 1:3). There are biblical instances of a father (II Sam. 13:31–38), a son (II Kings 14:5–6), brothers (Judg. 8:4–21; II Sam. 2:22–23), and also the king (I Kings 2:29–34) as avengers. It was later stipulated that when no next of kin was available or came forward, an avenger was to be appointed by the court (Sanh. 45b).
There is little doubt that legally the rights (and duties) of the blood-avenger became obsolete (Ḥavvat Ya'ir 146), though the killing by the avenger of a murderer is even today legally regarded by some scholars as no more than unintentional manslaughter (e.g. Keẓot ha-Ḥoshen ḤM 2). Apart from the law, the right and duty of avenging the blood of one's nearest relatives are still deeply imprinted on the mind and religious conviction of most Oriental (including many Jewish) communities; notwithstanding repeated efforts from various quarters, blood vengeance is not, however, recognized in Israeli law even in mitigating circumstances.
M. Duschak, Mosaisch-Talmudisches Strafrecht (1869), 19f.; S. Mayer, Rechte der Israeliten, Athener, und Roemer, 3 (1876), 36–47; E. Goitein, Vergeltungsprincip im biblischen und talmudischen Strafrecht (1891); G. Foerster, Das mosaische Strafrecht… (1900), 9ff.; J. Weismann, Talion und oeffentliche Strafe im mosaischen Rechte (1913); E. Merz, Blutrache bei den Israeliten (1916); ET, 5 (1953), 220–33; J.M. Ginzburg, Mishpatim le-Yisra'el (1956), 356–74; EM, 2 (1965), 392–4; B. Cohen, Jewish and Roman Law, 2 (1966), 624–7; addenda 793f.; I. Warhaftig, Goel ha-Dam, Tehumim, 11 (1990), 326-360.