Numbers 35:27-30 English Standard Version (ESV)

27. and the avenger of blood finds him outside the boundaries of his city of refuge, and the avenger of blood kills the manslayer, he shall not be guilty of blood.

28. For he must remain in his city of refuge until the death of the high priest, but after the death of the high priest the manslayer may return to the land of his possession.

29. And 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.

Numbers 35