What is the ruling on one who has issued an invalid judgment and then discovered its invalidity? Is expiation required of him? And is the lawyer who defends a criminal sinful?

The judge rules based on what he hears and does not know the unseen. He is rewarded if he strives and is correct, for him are two rewards, and if he errs, for him is one reward. There is no sin upon him if he is qualified for judgeship. If an error becomes clear to him, he must revoke the ruling and return to what is correct. He revokes the ruling if the error is in the Sharia ruling by contradicting a text, a consensus (ijma'), or a clear analogical deduction (qiyas jali), or if it was based on a non-existent reason such as false evidence, or if there was a defect in the procedure, such as ruling based on the testimony of two disbelievers.