Under the rule of law requiring the disclosure of exculpatory evidence announced in Brady v. Maryland, 373 U.S. 83 (1963) and then extended by the Supreme Court to include witness impeachment evidence in Giglio v. United States, 405 U.S. 150 (1972), the government is required to provide the defense with witness impeachment information that is in its possession or is discoverable.  In this case a witness could only identify the defendant after hypnosis … a fact that was withheld from the defense and therefore never considered by the jury.