Section II. Possession of Another's Property in Bad Faith

When one has wrongfully had possession of another’s property, well knowing that he had no right to keep it, on coming to a better frame of mind he is bound in the first place to restore the property itself to its rightful owner. Moreover, if the owner has suffered any special loss through being deprived of what belongs to him, the thief must make this good, inasmuch as he was the unjust cause of it. Furthermore, all natural or civil fruits of the property he must restore to the owner, for res fructificat domino; and if they have been consumed, their value must be given to him or else he will not have his own. Any fruits which are due to the industry of the thief, and all necessary and useful expenses which he incurred in respect of the property, he may in conscience deduct from what must be restored to the owner, for justice only prescribes that each one should have his own, not more than his own.

If another’s property is saved from fire, or from certain destruction in any other way, it still belongs to the former owner, for res clamat domino. At most, he who saved it has a claim to reasonable compensation for his trouble. If stolen goods perish in the hands of the thief, he must make restitution for them to the owner, unless they would have perished in the owner’s hands at the same time and in the same way. For if they would have perished at the same time and in the same way, the thief is not the cause of their destruction: otherwise he is, and he must bear the consequences.

If stolen property had different values after the theft, the owner’s losses must always be made good; and so if he intended to sell it when at its highest value, that value must be restored to him. Usually, however, if the property itself cannot be restored, it will be sufficient to restore the value which it had at the time of the theft. This is the teaching of many theologians and it seems to be in agreement with the provisions of English law: ‘‘ The measure of damages in an action for conversion is the actual loss sustained by the wrongful act. In general, this would be the market value of the goods at the time of conversion. ... And the jury on the trial of an action for conversion may also give damages in the nature of interest over and above the value of the goods converted.””