Discovery

In Weatherford v. Bursey, the U.S. Supreme Court stated that the defendant in a criminal case has no federal constitutional right to general discovery. However, in one particular area, the due process clause produces a limited constitutional right to discovery. The Supreme Court began the development of the constitutional right of the defense to disclosure in Mooney v. Holohan with a rule that the prosecution could obtain a conviction through deliberate deception by presentation of testimony that was known to be perjured. It expanded this concept substantially in Brady v. Maryland by holding that the prosecution violates due process where it fails to disclose to the defense evidence favorable to the accused that is material either to guilt or punishment. The Brady doctrine, as it is called, has been refined by a number of subsequent cases that limit its application to evidence that is "material" in that the evidence would have made a different result in the trial "reasonably probable" had it been disclosed.

Brady did not explicitly require any pretrial disclosure of the evidence. However, the general position adopted by most courts and commentators is that pretrial disclosure is required if advance disclosure is necessary for the evidence to be used effectively. Thus, if the exculpatory material requires defense development before it can be introduced, a constitutionally based discovery requirement is thereby created. The right of defendants under most rules to obtain discovery of information material to the preparation of the defense involves a statutory right to discovery of evidence that is substantially broader than the constitutional right.