Here the 1906 LDS edition emended the original lay to lying, thus changing the verb from lay to lie and the form of the verb from the infinitive to the present participle. This change was probably influenced by the fact that the following conjoined complement takes the present participial form: “and also Aaron and his brethren standing as though they had been the cause of his fall”. The change to lying was followed in the immediately following LDS editions and printings: the third printing (in 1907) of the 1905 Chicago missionary edition, the 1907 vest-pocket edition, and the 1911 large-print Chicago edition. However, the editors for the 1920 LDS edition intentionally restored the original verb form lay (the change is marked in the committee copy).
There are two issues here: (1) should the infinitive or the present participial form of the verb be used; and (2) which verb should be used, lie or lay? Let us first consider the question of whether the verb form should be the infinitive or the present participle. Elsewhere in the text, there are examples of the verb see taking either complement form, as in the following contrastive pair of examples:
In this contrasting pair there is not much difference between coming and come, but in other instances the infinitive implies the completion of an action while the present participial form implies a continuing action:
In the case of Alma 22:19, the context implies a continuing action (that is, the king is lying on the ground), so in modern English we expect the present participial form lying or laying. Interestingly, in the King James Bible, we have examples of both the infinitive and present participial forms for the verb lie in this construction, yet in each instance we have a continuing action:
Thus the occurrence of the infinitive form lay (or lie) in Alma 22:19 is quite possible and will be accepted in the critical text.
On the other hand, these biblical examples read with the verb lie rather than lay. Historically, lie is the intransitive verb form and, according to prescriptive grammar, is supposed to be used only intransitively, while lay is supposed to be the transitive form. Yet modern English speakers do not readily make this distinction. See, for instance, the discussion under lay in Merriam Webster’s Dictionary of English Usage. Also see the discussion under Omni 1:30 and more generally under lay in volume 3. The critical text will, of course, restore the original lay here in Alma 22:19.
Summary: Maintain the original use of the verb lay in Alma 22:19, although prescriptive grammarians prefer the intransitive lie; since the action is continuous in this passage, modern English speakers prefer the present participial form (lying or laying) over the infinitive form (lie or lay); the use of the infinitive form in Alma 22:19 is supported by usage in the King James Bible.