Objection 1. It would seem that he who has taken a thing is not always bound to restore it. Restitution re-establishes the equality of justice, by taking away from him that has more and giving to him that has less. Now it happens sometimes that he who has taken that which belongs to another, no longer has it, through its having passed into another's hands. Therefore it should be restored, not by the person that took it, but by the one that has it.
Objection 2. Further, no man is bound to reveal his own crime. But by making restitution a man would sometimes reveal his crime, as in the case of theft. Therefore he that has taken a thing is not always bound to restitution.
Objection 3. Further, the same thing should not be restored several times. Now sometimes several persons take a thing at the same time, and one of them restores it in its entirety. Therefore he that takes a thing is not always bound to restitution.
On the contrary, He that has sinned is bound to satisfaction. Now restitution belongs to satisfaction. Therefore he that has taken a thing is bound to restore it.
I answer that, With regard to a man who has taken another's property, two points must be considered: the thing taken, and the taking. By reason of the thing taken, he is bound to restore it as long as he has it in his possession, since the thing that he has in addition to what is his, should be taken away from him, and given to him who lacks it according to the form of commutative justice. On the other hand, the taking of the thing that is another's property, may be threefold. For sometimes it is injurious, i.e. against the will of the owner, as in theft and robbery: in which case the thief is bound to restitution not only by reason of the thing, but also by reason of the injurious action, even though the thing is no longer in his possession. For just as a man who strikes another, though he gain nothing thereby, is bound to compensate the injured person, so too he that is guilty of theft or robbery, is bound to make compensation for the loss incurred, although he be no better off; and in addition he must be punished for the injustice committed. Secondly, a man takes another's property for his own profit but without committing an injury, i.e. with the consent of the owner, as in the case of a loan: and then, the taker is bound to restitution, not only by reason of the thing, but also by reason of the taking, even if he has lost the thing: for he is bound to compensate the person who has done him a favor, and he would not be doing so if the latter were to lose thereby. Thirdly, a man takes another's property without injury to the latter or profit to himself, as in the case of a deposit; wherefore he that takes a thing thus, incurs no obligation on account of the taking, in fact by taking he grants a favor; but he is bound to restitution on account of the thing taken. Consequently if this thing be taken from him without any fault on his part, he is not bound to restitution, although he would be, if he were to lose the thing through a grievous fault on his part.
Reply to Objection 1. The chief end of restitution is, not that he who has more than his due may cease to have it, but that he who has less than his due may be compensated. Wherefore there is no place for restitution in those things which one man may receive from another without loss to the latter, as when a person takes a light from another's candle. Consequently although he that has taken something from another, may have ceased to have what he took, through having transferred it to another, yet since that other is deprived of what is his, both are bound to restitution, he that took the thing, on account of the injurious taking, and he that has it, on account of the thing.
Reply to Objection 2. Although a man is not bound to reveal his crime to other men, yet is he bound to reveal it to God in confession; and so he may make restitution of another's property through the priest to whom he confesses.
Reply to Objection 3. Since restitution is chiefly directed to the compensation for the loss incurred by the person from whom a thing has been taken unjustly, it stands to reason that when he has received sufficient compensation from one, the others are not bound to any further restitution in his regard: rather ought they to refund the person who has made restitution, who, nevertheless, may excuse them from so doing.
Source: Summa Theologica (New Advent)