John Gill Commentary Leviticus 5:3

"Or if he touch the uncleanness of man, whatsoever his uncleanness be wherewith he is unclean, and it be hid from him; when he knoweth of it, then he shall be guilty." — Leviticus 5:3 (ASV)

Or if he touch the uncleanness of man The dead body of a man, or the bone of a dead body, or a grave, or any profluvious or menstruous person:

whatsoever uncleanness [it be] that a man shall be defiled withal : not morally, but ceremonially:

and it be hid from him ; he is not sensible that he has touched any thing ceremonially unclean:

when he knoweth [of it], then he shall be guilty : acknowledge his guilt, and offer a sacrifice for it, as after directed.