What should I do with a debt I owe to a person who has died, when I do not know his heirs?

If a person is unable to identify the heirs of a deceased individual to whom they owe a debt, or who has a mortgage or a deposit with them, and they have exerted effort in searching without success, then they should give it as charity on behalf of the deceased for charitable purposes, such as to the poor, for the construction of mosques, or other Islamic projects, with the intention of benefiting the deceased. Alternatively, they may hand it over to the ruler or judge, obtaining a receipt, but spending it on charitable causes is more beneficial and quicker for its owner.