About five hundred years before the birth of the Savior, Nephi the son of Lehi had prophesied that at the coming of the Christ the law of Moses "shall be fulfilled." (2 Nephi 25:24.) Thus at the sign of the birth of Christ, some of the descendants of Nephi claimed "it was no more expedient to observe the law of Moses" because according to their interpretation of the scriptures the law of Moses had been fulfilled. (3 Nephi 1:24.) However, it was made known unto them "that the law was not yet fulfilled, and that it must be fulfilled in every whit." (3 Nephi 1:25.)
Later, during the three days between his crucifixion and resurrection, the Savior spoke to the righteous Nephites living on the American continent and said "in me is the law of Moses fulfilled." (3 Nephi 9:17.) Still later the resurrected Savior appeared to the Nephites and taught, ". . . verily I say unto you, one jot nor one tittle hath not passed away from the law, but in me it hath all been fulfilled." (3 Nephi 12:18.) Evidently the law of Moses was fulfilled by the Savior at the time of his crucifixion and resurrection.
(For further information on the topic "The Relationship Between the Law of Moses and the Atonement of Jesus Christ" see the material listed after 2 Nephi 25:20-30.)