Numbers 35:29-32

29And these things shall be for a statute and rule for you throughout your generations in all your dwelling places.

30"If anyone kills a person, the murderer shall be put to death on the evidence of witnesses. But no person shall be put to death on the testimony of one witness.

31Moreover, you shall accept no ransom for the life of a murderer, who is guilty of death, but he shall be put to death.

32And you shall accept no ransom for him who has fled to his city of refuge, that he may return to dwell in the land before the death of the high priest.