What should I do with a gift I received to which I am not entitled, especially given that I have no connection to the giver?

If the gift does not belong to the giver, it must be returned to its original owner. If it was given in exchange for a sin, and the giver achieved his purpose, then it must be disposed of by spending it on the poor, the needy, and for the benefit of Muslims; otherwise, it must be returned to him. However, if it was obtained through usurpation or theft and its owners cannot be identified, then it must be given in charity on behalf of its owner, with a guarantee to him should he be found.