Praise be to Allah.
In the case of property lost in the Haram, it is not permissible for anyone to take it except the one who identifies it (the owner), because the Prophet (peace and blessings of Allaah be upon him) said: “Anything that is dropped there is not permissible for anyone except the owner who identifies it.” (Agreed upon)
The person mentioned has to return the property in question to the Supreme Court in Makkah to that they can hand it over to the committee responsible for property lost in the Haram. Thus he will free himself from blame, so long as he also repents to Allaah for his shortcomings if he did not announce the lost property in the past. And Allaah is the source of strength.