Deuteronomy 21:1
If one be found slain in the land which the LORD thy God giveth thee to possess it, lying in the field, and it be not known who hath slain him: If one be found slain in the land which the LORD thy God giveth thee to possess it, lying in the field, and it be not known who hath slain him:
The law opens with the case of a murdered body discovered lying out in open country inside the territory given to Israel for possession, where the identity of the killer cannot be established. That discovery does not leave the death as a private misfortune but triggers a prescribed legal response. The response is a solemn public inquiry and atoning ceremony carried out under the direction of the elders, the judges, and the priests.
The ceremony is a public testimony that the rulers regard the shedding of blood with abhorrence rather than indifference. It forbids carelessness or neglect toward the crime and lays upon them the duty to exert every possible effort to find the wrongdoer and bring him to justice. Behind the requirement stands the principle that unpunished murder pollutes the land itself. Those in authority who through negligence shield the guilty become partakers in the guilt.