Charles Ellicott Commentary Leviticus 5:2

"Or if any one touch any unclean thing, whether it be the carcass of an unclean beast, or the carcass of unclean cattle, or the carcass of unclean creeping things, and it be hidden from him, and he be unclean, then he shall be guilty." — Leviticus 5:2 (ASV)

Or if a soul touch any unclean thing. —The second instance presented which requires this sacrifice is the case of anyone touching the dead body of a clean animal, or the living or dead body of an unclean animal or reptile.

And if it be hidden from him. —That is, if he, through carelessness, forgot that he had contracted this defilement; as the Vulgate rightly paraphrases it, “and forgets his uncleanness.” The touching of a carcass simply involved uncleanness until evening, which the washing of the person and his garments thus defiled sufficed to remove (Leviticus 11:24; Leviticus 11:31). It was only when thoughtlessness made him forget his duty, and when reflection brought to his mind and conscience the violation of the law, that he was required to confess his sin and bring a trespass offering.

He also shall be unclean, and guilty. —Better, and he is unclean, and acknowledges that he is guilty (Leviticus 4:22). The Greek Version, called the Septuagint, which is the most ancient translation of the Hebrew Scriptures, omits altogether the latter part of this verse, which is represented in the Authorized Version by and if it be hidden from him, he also shall be unclean and guilty, thus showing that the Hebrew manuscript or manuscripts from which this old version was made did not have this clause. This is, moreover, supported by the fact that it needlessly anticipates the summary formula of the next verse, which continues the subject, and where it appears in its proper place.