Ancient Israelite law allowed for the execution of people by hanging them on a tree. It was a type of crucifixion. We tend to think that victims were hanged by a noose; however, they also could hang them by their arms. One way or another when people were crucified by hanging on a tree they died of asphyxiation; they could not breathe. Eventually, their diaphragm became exhausted and they were unable to breathe anymore. That may be how Jesus died. He took his last breath and said “Into thy hands I commend my spirit” (Luke 23:46), and he died.
The detail here about how they killed this robber informs us that they were well aware of this mode of crucifixion or execution. Zenos and Zenock prophesied that Jesus would be crucified. Here in 3 Nephi, leading up to the point when they see the signs of the death of Christ there is a little more information on the topic.
In later Jewish law, once someone had been crucified on a tree, according to the Rabbis, the tree must be chopped down. The reason is that you want to remove from all memory the wickedness of this person who had been so ignominiously put to death. Eventually, some pointed out that they would not have many trees left if they did that. The Rabbis determined that it was acceptable to use a post as a substitute for a tree. Here among the Nephites, there appeared to be plenty of trees around, so they still chopped the tree down as a symbol of bringing Zemnarihah down, and also so that his memory would be obliterated.
I have asked several scholars if they have ever heard of any passages, other than the one in the medieval Maimonides, that talks about chopping down the tree on which a criminal was executed so that people would not have to see the tree and be reminded of that wicked person. None have ever said that they had ever seen or heard of this practice anywhere else. When I showed one scholar in particular this instance in the Book of Mormon, he said, “Well, … that is really interesting.”
Book of Mormon Central, “Why Did the People Cut Down the Tree after Hanging Zemnarihah? (3 Nephi 4:28),” KnoWhy 192 (September 21, 2016).
John W. Welch, “Judicial Punishments: Types and Rationales: Hanging on a Tree (and Crucifixion),” in The Legal Cases in the Book of Mormon(Provo, UT: BYU Press, 2008), 352–354.
W. Reid Litchfield, “The Search for the Physical Cause of Jesus Christ’s Death,” BYU Studies 37 no. 4 (1997–1998), 93–109.
John W. Welch, “The Execution of Zemnarihah,” in Reexploring the Book of Mormon: A Decade of New Research, ed. John W. Welch (Salt Lake City and Provo, UT: Deseret Book and FARMS, 1992), 250–252.