Objection 1. It would seem that restitution is not binding on those who have not taken. For restitution is a punishment of the taker. Now none should be punished except the one who sinned. Therefore none are bound to restitution save the one who has taken.
Objection 2. Further, justice does not bind one to increase another's property. Now if restitution were binding not only on the man who takes a thing but also on all those who cooperate with him in any way whatever, the person from whom the thing was taken would be the gainer, both because he would receive restitution many times over, and because sometimes a person cooperates towards a thing being taken away from someone, without its being taken away in effect. Therefore the others are not bound to restitution.
Objection 3. Further, no man is bound to expose himself to danger, in order to safeguard another's property. Now sometimes a man would expose himself to the danger of death, were he to betray a thief, or withstand him. Therefore one is not bound to restitution, through not betraying or withstanding a thief.
On the contrary, It is written (Romans 1:32): "They who do such things are worthy of death, and not only they that do them, but also they that consent to them that do them." Therefore in like manner they that consent are bound to restitution.
I answer that, As stated above (Article 6), a person is bound to restitution not only on account of someone else's property which he has taken, but also on account of the injurious taking. Hence whoever is cause of an unjust taking is bound to restitution. This happens in two ways, directly and indirectly. Directly, when a man induces another to take, and this in three ways. First, on the part of the taking, by moving a man to take, either by express command, counsel, or consent, or by praising a man for his courage in thieving. Secondly, on the part of the taker, by giving him shelter or any other kind of assistance. Thirdly, on the part of the thing taken, by taking part in the theft or robbery, as a fellow evil-doer. Ondirectly, when a man does not prevent another from evil-doing (provided he be able and bound to prevent him), either by omitting the command or counsel which would hinder him from thieving or robbing, or by omitting to do what would have hindered him, or by sheltering him after the deed. All these are expressed as follows:
"By command, by counsel, by consent, by flattery, by receiving, by participation, by silence, by not preventing, by not denouncing."
It must be observed, however, that in five of these cases the cooperator is always bound to restitution. First, in the case of command: because he that commands is the chief mover, wherefore he is bound to restitution principally. Secondly, in the case of consent; namely of one without whose consent the robbery cannot take place. Thirdly, in the case of receiving; when, to wit, a man is a receiver of thieves, and gives them assistance. Fourthly, in the case of participation; when a man takes part in the theft and in the booty. Fifthly, he who does not prevent the theft, whereas he is bound to do so; for instance, persons in authority who are bound to safeguard justice on earth, are bound to restitution, if by their neglect thieves prosper, because their salary is given to them in payment of their preserving justice here below.
In the other cases mentioned above, a man is not always bound to restitution: because counsel and flattery are not always the efficacious cause of robbery. Hence the counsellor or flatterer is bound to restitution, only when it may be judged with probability that the unjust taking resulted from such causes.
Reply to Objection 1. Not only is he bound to restitution who commits the sin, but also he who is in any way cause of the sin, whether by counselling, or by commanding, or in any other way whatever.
Reply to Objection 2. He is bound chiefly to restitution, who is the principal in the deed; first of all, the "commander"; secondly, the "executor," and in due sequence, the others: yet so that, if one of them make restitution, another is not bound to make restitution to the same person. Yet those who are principals in the deed, and who took possession of the thing, are bound to compensate those who have already made restitution. When a man commands an unjust taking that does not follow, no restitution has to be made, since its end is chiefly to restore the property of the person who has been unjustly injured.
Reply to Objection 3. He that fails to denounce a thief or does not withstand or reprehend him is not always bound to restitution, but only when he is obliged, in virtue of his office, to do so: as in the case of earthly princes who do not incur any great danger thereby; for they are invested with public authority, in order that they may maintain justice.
Source: Summa Theologica (New Advent)