According to an article by Kelly Ward and John Welch, the legal distinctions between theft and robbery, especially under the laws of ancient Israel, have been analyzed thoroughly by Bernard S. Jackson, Professor of Law at the University of Kent-Canterbury and editor of Jewish Law Annual. He shows, for example, how robbers usually acted in organized groups rivaling local governments and attacking towns and how they swore oaths and extorted ransom, a menace worse than outright war. Thieves, however, were a much less serious threat to society.
According to recent studies, the details of these ancient legal and linguistic distinctions are observable in the Book of Mormon. Here in the midst of describing actions against the Gadianton robbers, Joseph Smith the translator did not commit any errors by inserting the word "thieves" (see the word "robber" in 3 Nephi 3:12) that someone would if he were fabricating the story from an Anglo-American perspective. [Kelly Ward and John W. Welch, "Thieves and Robbers," in Reexploring the Book of Mormon, pp. 248-249] [See the commentary on how Laban called the sons of Lehi "robbers" -- 1 Nephi 3:13]