Moira Juvenile Law Lawyer, New York

A lawyer who is elected to represent a state government in criminal cases in a designated county or judicial district. A D.A.'s duties typically include reviewing police arrest reports, deciding whether to bring criminal charges against arrested people and prosecuting criminal cases in court. The D.A. may also supervise other attorneys, called Deputy District Attorneys or Assistant District Attorneys. In some states a District Attorney may be called a Prosecuting Attorney, County Attorney or State's Attorney. In the federal system, the equivalent to the D.A. is a United States Attorney. The country has many U.S. Attorneys, each appointed by the President, who supervise regional offices staffed with prosecutors called Assistant United States Attorneys.

One of the most sacred principles in the American criminal justice system, holding that a defendant is innocent until proven guilty. In other words, the prosecution must prove, beyond a reasonable doubt, each element of the crime charged.

Latin for 'we shall no longer prosecute.' At trial, this is an entry made on the record by a prosecutor in a criminal case stating that he will no longer pursue the matter. An entry of nolle prosequi may be made at any time after charges are brought and before a verdict is returned or a plea entered. Essentially, it is an admission on the part of the prosecution that some aspect of its case against the defendant has fallen apart. Most of the time, prosecutors need a judge's A1:C576 to 'nol-pros' a case. (See Federal Rule of Criminal Procedure 48a.) Abbreviated 'nol. pros.' or 'nol-pros.'

Latin for a 'guilty act.' The actus reus is the act which, in combination with a certain mental state, such as intent or recklessness, constitutes a crime. For example, the crime of theft requires physically taking something (the actus reus) coupled with the intent to permanently deprive the owner of the object (the mental state, or mens rea).

The earliest and most common test for criminal insanity, in which a criminal defendant is judged legally insane only if he could not distinguish right from wrong at the time he committed the crime. For example, a delusional psychotic who believed that his assaultive acts were in response to the will of God would not be criminally responsible for his acts.

The privilege that allows the president and other high officials of the executive branch to keep certain communications private if disclosing those communications would disrupt the functions or decisionmaking processes of the executive branch. As demonstrated by the Watergate hearings, this privilege does not extend to information germane to a criminal investigation.

A procedure in which the police place a suspect in a line with a group of other people and ask an eyewitness to the crime to identify the person he saw at the crime scene. The police are supposed to choose similar-looking people to appear with the suspect. If the suspect alone matches the physical description of the perpetrator, evidence of the identification can be attacked at trial. For example, if the robber is described as a Latino male, and the suspect, a Latino male, is placed in a lineup with ten white males, a witness' identification of him as the robber will be challenged by the defense attorney.

A formal investigation -- governed by court rules -- that is conducted before trial. Discovery allows one party to question other parties, and sometimes witnesses. It also allows one party to force the others to produce requested documents or other physical evidence. The most common types of discovery are interrogatories, consisting of written questions the other party must answer under penalty of perjury, and depositions, which involve an in-person session at which one party to a lawsuit has the opportunity to ask oral questions of the other party or her witnesses under oath while a written transcript is made by a court reporter. Other types of pretrial discovery consist of written requests to produce documents and requests for admissions, by which one party asks the other to admit or deny key facts in the case. One major purpose of discovery is to assess the strength or weakness of an opponent's case, with the idea of opening settlement talks. Another is to gather information to use at trial. Discovery is also present in criminal cases, in which by law the prosecutor must turn over to the defense any witness statements and any evidence that might tend to exonerate the defendant. Depending on the rules of the court, the defendant may also be obliged to share evidence with the prosecutor.

A mental defect or disease that makes it impossible for a person to understand the wrongfulness of his acts or, even if he understands them, to ditinguish right from wrong. Defendants who are criminally insane cannot be convicted of a crime, since criminal conduct involves the conscious intent to do wrong -- a choice that the criminally insane cannot meaningfully make. See also irresistible impulse; McNaghten Rule.