“A `garb of secrecy’ is surely a formidable instrument with which to stab a man!”
M. T. Lamb, The Golden Bible (1887), 57.
“`Garb’ is clothing; one cannot be stabbed with a piece of clothing—it would be even more difficult for someone to be stabbed with that!”
Weldon Langfield, The Truth About Mormonism (1991), 50.
John Tvedtnes and David Bokovoy offer the following insight:
In Helaman 9:6, we read that the Nephite judge had been "stabbed by his brother by a garb of secrecy." Critics have contended that this makes no sense in English since "garb" has the same meaning as "garment" or "clothing." This idiom is the same as the English "under cloak of secrecy." But what is most interesting is that the Hebrew word beged means both "garment" or "garb" (e.g. Genesis 39:12-13) and "treachery." This is an obvious word-play in the Hebrew original of the Book of Mormon. As for the preposition by, in Hebrew its range of meaning includes "in," "with," and "by means of."
David E. Bokovoy and John A. Tvedtnes, Testaments: Links Between the Book of Mormon and the Hebrew Bible (2003), 204.