How can the deceased be absolved from the money he acquired from selling spare parts for the state's car, the amount of which his family does not know?

The amount due can be determined by contacting the entity that granted the car. If that is not possible and the entity does not know the amount missing, then precaution should be taken to pay the right [amount] until one's conscience is cleared. The right should be paid to the relevant state authority if possible. Otherwise, it should be given as charity to the poor and needy, or spent on general Muslim welfare. This should be done promptly to settle the deceased's rights, as the Prophet, peace and blessings be upon him, said: "The soul of a believer is tied to his debt until it is paid off."