Since 1963, a series of U.S. Supreme Court decisions has clarified that, in a criminal case, prosecutors must disclose to the defense evidence favorable to the defendant. This includes information that may be used to impeach the credibility of government witnesses, including law enforcement officers. These decisions mean that officers who have documented histories of lying in official matters, falsifying reports, or expressing bias may become even greater liabilities to their agencies because their records may render them unable to testify credibly and consequently unable to work effectively as law enforcement officers.