What should I do with money that was seized by the state, had been allocated for trade, and then its owner died and I do not know his address, and that money has been returned to me?

If the state seizes partnership funds due to your negligence and without your partner's knowledge, you are liable for the money and must return it to the partner's heirs, whether or not the money is returned to you. However, if the seizure was without negligence on your part, you are not obliged to guarantee the money unless it is returned to you. When the money is returned, it belongs to the heirs, and they must be informed of this. They then have the option to maintain the partnership or to claim their share. You must search for the partner's heirs to deliver the trust to them. If they cannot be found after diligent effort, it is permissible to give the money in charity on their behalf, while their right to claim it remains if they appear later.