Actually, he can be charges with Larceny just as if he purposley stole it. According to most states penal laws, "finders keepers" is not a valid theory. It is larceny to "with the intent to deprive another of property... he wrongfully takes, obtains, or withols such property from the owner thereof".

NY Penal Law, § 155.05 (2b) specifically mentions that aquirnig lost property without making a reasonable attempt to find the owner and return it to him. Since the item is worth one thousad dollars or less it is defined as Peitit Larceny by § 155.25. That is an A Misdameanor.

So eyecue, feel free to press charges (but paying for his lock is more statesmenlike)