The 1841 British edition removed the repeated preposition of in this postmodifying phrase, thus producing “the secret work of murder and robbery”. The use of the repeated preposition is characteristic of the Book of Mormon text. For the phrase “work of”, the of is typically repeated for a following conjoined noun phrase; there is only one case where it is not (marked below with an asterisk):
The critical text will maintain the repeated of here in Helaman 2:4. For further discussion and examples of prepositional repetition, see under conjunctive repetition in volume 3.
Summary: Maintain in Helaman 2:4 the repeated of in the conjunctive prepositional phrase “of murder and of robbery”, the reading of both manuscripts and the first three editions.