Discovery

While typically going further, most modern criminal discovery rules in the United States cover several core types of information, which were generally provided to defendants in the first generation of discovery statutes and rules. This core includes the statements of the defendant, documents, and tangible objects that either the prosecution intends to introduce at trial or were obtained from the defendant, and scientific reports of witnesses that the prosecution intends to call at trial. These items have several characteristics. First, they are often the key elements of the criminal case and defense access is arguably essential to effective testing of the prosecution's case. Second, the evidence often came from the defendant and providing discovery of it seems not only fair but also reveals no prosecution secrets. Third, the evidence provides limited opportunities for effective perjury and even less chance of witness tampering.

One of the most important types of evidence in criminal cases is that of statements made by the defendant. Without exception, the prosecution is required to provide such statements when made by the defendant to individuals then known by the defendant to be law enforcement officials. However, in some jurisdictions, when such statements were made to others, such as undercover agents, they need not be disclosed, and are withheld lest witness identities, not otherwise discoverable, be revealed.

The defendant's criminal record is often added to this core because of its obvious usefulness in trial decisions and the fact that the prosecution has better access to this unalterable type of information. Also typically included is a provision for discovery of evidence material to the preparation of the defense. Obtaining discovery of this latter type requires a showing by the defendant that the evidence is important under the facts of the particular case to adequate preparation of a defense. The effectiveness of this provision depends on the defense having knowledge of the case which, given limited discovery, may not be available, and rests ultimately on the relative liberality of prosecutors and judges, who exercise substantial discretion over this class of discovery.

In addition to the defendant's own statements, some jurisdictions provide those of codefendants. This is the point where systems begin to differentiate themselves as far as their attitude toward discovery. In a number, the information is seen as presenting opportunities for effective fabrication of testimony, and disclosure is not provided unless it can be shown to be material to the preparation of a defense, such as showing a need to have separate trials.

Providing discovery in these core areas to the defense often comes today with basic obligations of reciprocity. Whether conditional upon defense requests for, and prosecution delivery of, similar information from the prosecution or an independent right of the prosecution, a general feature of modern criminal discovery is that the defendant must provide the prosecution with documents and tangible objects that it intends to introduce and with relevant reports of expert witnesses it intends to call.