The Book of Mormon refers to both “thieves” and “robbers”. While most readers would not notice any difference between the two, John W. Welch explains the significance:
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 the 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.
Recently studies have shown in detail how the ancient legal and linguistic distinctions are also observable in the Book of Mormon. This explains how Laban could call the sons of Lehi “robbers” and threaten to execute them on the spot without a trial, for that is how a military officer like Laban no doubt would have dealt with a robber. It also explains why the Lamanites are always said to “rob” from the Nephites but never from their own brethren—that would be “theft,” not “robbery.” It also explains the rise and fearful menace of the Gadianton society, who are always called “robbers” in the Book of Mormon, never “thieves.”– John W. Welch and Kelly Ward – Thieves and Robbers
How would Joseph Smith be so consistent in the correct usages of these two terms even when the Bible wasn’t?