Have found that which was lost - The Roman lawyers laid it down as a sound maxim of jurisprudence, "that he who found any property and applied it to his own use, should be considered as a thief whether he knew the owner or not; for in their view the crime was not lessened, supposing the finder was totally ignorant of the right owner." Qui alienum quid jacens lucri faciendi causa sustulit, furti obstringitur, sive scit, cujus sit, sive ignoravit; nihil enim ad furtum minuendum, facit, quod, cujus sit, ignoret - Digestor, lib. xlvii., Titus. ii., de furtis, Leg. xliii., sec. 4. On this subject every honest man must say, that the man who finds any lost property, and does not make all due inquiry to find out the owner, should, in sound policy, be treated as a thief. It is said of the Dyrbaeans, a people who inhabited the tract between Bactria and India, that if they met with any lost property, even on the public road, they never even touched it. This was actually the case in this kingdom in the time of Alfred the Great, about a. d. 888; so that golden bracelets hung up on the public roads were untouched by the finger of rapine. One of Solon's laws was, Take not up what you laid not down. How easy to act by this principle in case of finding lost property: "This is not mine, and it would be criminal to convert it to my use unless the owner be dead and his family extinct." When all due inquiry is made, if no owner can be found, the lost property may be legally considered to be the property of the finder.

Or have found that which was lost, and lieth concerning it, and sweareth falsely; in any of all these that a man doeth, (c) sinning therein:
(c) In which he cannot but sin: or, in which a man accustoms to sin by perjury or such like thing.

Or have found that which was lost, and lieth concerning it,.... Who having found anything lost, at once concludes it his own, and converts it to his own use, never inquiring after the proprietor of it, or taking any method to get knowledge of him, and restore it to him; but so far from that, being suspected of finding it, and charged with it denies it: Maimonides (k) gives a reason why a lost thing should be restored, not only because so to do is a virtue in itself praiseworthy, but because it has a reciprocal utility; for if you do not restore another's lost things, neither will your own be restored to you:
and sweareth falsely; which is to be understood, not of the last case only, but of all the rest, or of anyone of them, as it follows:
in any of all these that a man doeth, sinning therein; by unfaithfulness in a trust, cheating, defrauding, lying, and false swearing.
(k) Moreh Nevochim, par. 3. c. 40.

Swear falsely - His oath being required, seeing there was no other way of discovery left.