Numbers 35:28

35:28 because the slayer should have stayed in his town of refuge until the death of the high priest. But after the death of the high priest, the slayer may return to the land of his possessions.

Numbers 35:30

35:30 “Whoever kills any person, the murderer must be put to death by the testimony of witnesses; but one witness cannot testify against any person to cause him to be put to death.