Numbers 35:21

or if you beat your enemy to death with your bare hands, you must be put to death. You are a murderer. The relative who can avenge the death must kill you when he catches up with you, because you are a murderer.

Treasury of Scripture Knowledge

Summary

Or in enmity smite him with his hand, that he die: he that smote him shall surely be put to death; for he is a murderer: the revenger of blood shall slay the murderer, when he meeteth him.

General references

Bible References

General references

Numbers 35:19
The relative who can avenge the death must make sure a murderer is put to death. When he catches up with the murderer, he must kill him.