Numbers 19:16

19:16 And whoever touches the body of someone killed with a sword in the open fields, or the body of someone who died of natural causes, or a human bone, or a grave, will be unclean seven days.

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.