You have to do your utmost to find the owner of this trust. If you cannot find him then donate it to some charitable cause, with the intention of giving charity on behalf of the owner. If the owner or his heir comes along after that, then tell him what you have done. If he approves of that, all well and good, but if he does not approve, give him the equivalent amount, and you will have the reward for what you gave in charity, Insha Allah.