Numbers 35:16

But if he struck him down with an iron object , so that he died , he is a murderer . The murderer shall be put to death .

“‘If anyone strikes someone a fatal blow with an iron object, that person is a murderer; the murderer is to be put to death.

And if he smite him with an instrument of iron, so that he die, he is a murderer : the murderer shall surely be put to death.