[Ruling on Purchasing Goods the Buyer Fears May Be Looted]

The answer—and by Allah’s enabling: If the buyer thinks it likely that what is offered for sale is among what looters wrongfully took from its owners, it is not permissible for him to buy it.
 And if he does not think it likely that it is looted, it is permissible for him to buy it. If, after purchasing it, it becomes clear to him that it is looted, then if he knows its owners he must return it to them; but if he cannot identify them and has despaired of doing so, he should dispose of it in the public interest.
 The evidence that the purchaser of a usurped or looted item is in the ruling of the usurper is Allah’s saying: “And do not consume one another’s wealth unjustly.” [Al-Baqarah:188] and the hadith, “The property of a Muslim is unlawful [to take] except with his willing consent.” Thus, whoever buys an item from a usurper is deemed a usurper; he does not acquire ownership by purchasing from the usurper, and the item remains the property of the one from whom it was usurped; frequent transfers from one buyer to another do not remove it from his ownership.
 If the buyer is in doubt whether the item is usurped or not, and neither possibility outweighs the other, it is better for him to leave it; in leaving it lies safety for his religion and his worldly affairs.
 If it is more likely to him that it is not usurped, it is permissible for him to buy it. The buyer is not required to abandon the item due to a weak possibility that it is usurped or looted. Were one obliged to act on such a weak conjecture, no item could ever be purchased in the market or elsewhere, for every item bears the possibility of being usurped or looted; a man would also refrain from accepting gifts and charity, and would refrain from eating from other people’s food for the same reason.
If it is said: The apparent presumption about one whose hand holds a thing is that he owns it, and Muslim judges rule for the possessor in the absence of a disputant—
We say: This presumption is shaken and weakened by the indications that what is offered for sale is looted or usurped.
The evidentiary value of possession for ownership is probabilistic, and the indications of usurpation and looting are also probabilistic; when the evidence for permissibility and the evidence for prohibition come together, acting on the prohibition is preferred.
Source: Min Thimār al-ʿIlm wa al-Ḥikmah vol.2