What is the ruling on paying money to a lawyer to defend a guilty prisoner, and when is such payment Islamically permissible and when is it not?

A lawyer is not permitted to defend except what is just, based on the prophetic tradition: "Whoever aids in falsehood to refute a truth with that falsehood has disavowed himself from the protection of Allah and His Messenger." The truth of a case, as opposed to its falsehood, can be ascertained by consulting scholars. The payment of the lawyer's fee follows the origin of the case: it is permissible to pay it if the case is just, and impermissible if it is false.