In the printer’s manuscript, Oliver Cowdery initially wrote “in a sepulchre”; then he supralinearly inserted to, thus changing the in to into. The 1830 typesetter, however, ignored this change and restored the earlier in. Oliver’s correction in 𝓟 appears to be virtually immediate (there is no change in the level of ink ﬂow), so most probably the original manuscript actually read into. On the other hand, the King James Bible supports the use of the preposition in with the verb lay and the noun sepulchre:
The well-known language referring to the burial of Christ seems to have been the source for the tendency in Alma 19:1 to adopt the phraseology “to lay in a sepulchre”. There is also a similar example in the Book of Mormon of the use of in with sepulchre:
See under that passage for discussion of the passive phraseology “to be laid in a sepulchre”.
Similarly, the scriptures consistently support the use of in when the verb is bury (“to bury in a sepulchre”) in 14 passages in the King James Bible as well as one in the Book of Mormon, again referring to the burial of Christ:
Further support for in comes from a nearby example in Alma 19 involving the verb place:
Despite all this support for in, the corrected into seems to have been the reading of the original manuscript, for there is clearly no motivation for Oliver Cowdery to have corrected the expected in to into except that 𝓞 read that way. Of course, it is possible that the reading in 𝓞 itself may have been faulty. There are quite a few examples in the history of the text of into and in being mixed up; for a list of examples, see under 1 Nephi 4:33. But overall, the reading with into is not impossible. Thus the critical text will accept the difficult reading with the preposition into here in Alma 19:1 since it will work and it seems to be intended. For another example in the Book of Mormon text where readers expect in rather than an original into, see the discussion under Mosiah 23:26; this passage originally read “the brethren of Alma … gathered themselves together into the city of Helam”, but the LDS text now has the expected in.
Summary: Restore the original but unexpected preposition into in Alma 19:1: “they were about to take his body and lay it into a sepulchre”.