Is it permissible to buy goods from government employees who are selling items they took from their offices?

If you know that the person bringing you the goods is a dishonest employee who unlawfully seizes what does not belong to him, then it is not permissible for you to buy from him or deal with him concerning the very thing he has unlawfully seized, otherwise, you would be like him. However, if the employee is authorized to dispose of what is under his control, then there is no harm in you buying from him.