Is it permissible for someone who found a bag of gold, and a year has passed, to utilize it, claiming that the one who lost it will come to inform the mosque's imam about it, with the possibility of giving him a portion of it?

We understand that the person used the found item (Luqata) after it remained with him for a full year and he did not publicize it. What this person did is a major mistake, a betrayal of trust, and a violation of Islamic law, for which he is sinful. He must hasten to repent to Allah Almighty, and know that this found item is a debt upon him and a trust around his neck that he must fulfill if its owner comes. He must now publicize it and make it known in places where its owner might be found. If its owner comes and identifies it, he must return it to him.