What is the ruling on returning a trust to someone who stole something and claimed it was a trust with him, and must it be returned to its rightful owner?

It is obligatory to return the stolen item to its owner, not to the thief. This is because whoever is able to return a consumed item from another's property held by a thief, or to inform its owner about it, but fails to do so, is liable. Thus, whoever is able to prevent injustice, stop it, and give every rightful person their due, but fails to do so, has been able to denounce evil but has not done so.