Am I obliged to return stolen financial trusts to their owner from my own money, and is it permissible for me to return them from bank interest?

The trustworthy hand does not guarantee unless it transgresses or is negligent. If the entrusted item perishes without negligence from the trustee, there is no guarantee upon him. If you were negligent in safeguarding the trust or transgressed by using it, then you are a guarantor and you guarantee it from your own money. As for usurious interests, they are not owned by the borrower of usury; rather, they should be spent on charitable causes and for the benefit of Muslims, knowing that dealing with usurious banks is forbidden (haram).