Responsa for Bava Kamma 115:8

Q. A's house was robbed and he reported this in town. Subsequently, he recognized one of his books in B's possession B had bought the book from C who had bought it from a Gentile. Moreover, A does not usually sell his books. B, therefore, stated under oath the price he paid for the book; but A constantly deferred payment of that amount.
A. A owes that amount to B. Since the court has a right to distrain a debtor's article for the benefit of the creditor, the court may surely confirm B in the possession of the book after the latter pays to A the difference between its actual value and the price he had originally paid. If B paid C for the book more than the latter paid to the Gentile, C must return the difference to A.
SOURCES: Am II. 138.

Q. A was robbed of his books during a riot. The books were later recognized in B's possession. Must B return the books to A upon receiving the amount he paid to the robbers?
A. Since the books were taken by Gentile robbers, A did not lose hope of retrieving them (B. K. 114a) and thus legally retained title to his books. Therefore, B must return the books to A. B is not entitled to any compensation, since it was common knowledge that A was robbed of his books, and since B bought them from known robbers.
This Responsum is addressed to "my teacher Rabbi Eliakim."
SOURCES: Pr. 1009; Cr. 196–7; Mord. B. K. 163.

Q. A fire, a veritable conflagration, broke out in town and people fled in fear thereof. A, however, braved the fire and saved a book the owners of which had already fled.
A. A is under no obligation to return the book to its owners, for as soon as the latter gave up hope of saving the book, it became abandoned property.
SOURCES: Cr. 251; Mord. B. K. 171; Mordecai Hagadol p. 392d; Hag. Maim., Gezelah 12, 6; Agudah B. K. 140.

Q. B claims that he gave A fifteen pounds to lend it on interest for two years and then give the principal and the interest to B's son if he should consent to marry A's daughter. B's son, however, refused to marry A's daughter and B wants his money back. A claims that he had originally accepted B's money as a dowry for his daughter, that he had taken possession of the gift for her, and that the money, therefore, belongs to her.
A. A dowry gift becomes the property of the donee only if the marriage takes place. Therefore, neither A nor his daughter has ever gained title to B's money, and A must return the principal plus the interest to B. Even if B expressly stipulated that he will forfeit the 15 pounds if the marriage does not take place, such a stipulation is considered an Asmakhta and is not valid. B, however, must pay A for his trouble in managing B's investments.
SOURCES: Cr. 86; Pr. 285; Mord. B.B. 615; Agudah B.B. 198.

Q. A's heirs demand from B A's Humash (one book of the Pentateuch) which witnesses saw in B's possession. B claims that A deposited the book with him as security for the two marks A owed him. Some of A's heirs admit having heard A say before his death that the book was deposited with B as a pledge. Is a Humash classified as an object which is usually borrowed or hired and regarding which a person is, therefore, not believed when he claims to have received it as a pledge?
A. Throughout the kingdom, Rashi's view is accepted that a Humash is not an object that is usually borrowed or hired. B therefore may take an oath that the book was pledged with him for two marks. However, B should be careful in taking his oath; for, if A did not actually owe him two marks, but promised to give B two marks if the latter effect a reconciliation between A and his son, A became indebted to B only for the latter's wages for the time and effort expended, but not for full two marks.
SOURCES: Pr. 1007.