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The mental component of criminal liability. To be guilty of most crimes, a defendant must have committed the criminal act (the actus reus) in a certain mental state (the mens rea). The mens rea of robbery, for example, is the intent to permanently deprive the owner of his property.

A decision by the jury to acquit a defendant who has violated a law that the jury believes is unjust or wrong. Jury nullification has always been an option for juries in England and the United States, although judges will prevent a defense lawyer from urging the jury to acquit on this basis. Nullification was evident during the Vietnam war (when selective service protesters were acquitted by juries opposed to the war) and currently appears in criminal cases when the jury disagrees with the punishment--for example, in 'three strikes' cases when the jury realizes that conviction of a relatively minor offense will result in lifetime imprisonment.

A court official usually classified as a peace officer (sometimes as a deputy sheriff, or marshal) and usually wearing a uniform. A bailiff's main job is to maintain order in the courtroom. In addition, bailiffs often help court proceedings go smoothly by shepherding witnesses in and out of the courtroom and handing evidence to witnesses as they testify. In criminal cases, the bailiff may have temporary charge of any defendant who is in custody during court proceedings.

A prosecution for murder in which the jury is also asked to decide if the defendant is guilty and, if he is, whether he should be put to death. When a prosecutor brings a capital case (also called a death penalty case), she must charge one or more 'special circumstances' that the jury must find to be true in order to sentence the defendant to death. Each state (and the federal government) has its own list of special circumstances, but common ones include multiple murders, use of a bomb or a finding that the murder was especially heinous, atrocious or cruel.

The component parts of crimes. For example, 'Robbery' is defined as the taking and carrying away of property of another by force or fear with the intent to permanently deprive the owner of the property. Each of those four parts is an element that the prosecution must prove beyond a reasonable doubt.

A crime that occurs when one person tries to physically harm another in a way that makes the person under attack feel immediately threatened. Actual physical contact is not necessary; threatening gestures that would alarm any reasonable person can constitute an assault. Compare battery.

A minor violation of the law that is punishable only by a fine--for example, a traffic or parking ticket. Not all vehicle-related violations are infractions, however--refusing to identify oneself when involved in an accident is a misdemeanor in some states.

Someone who helps another person (known as the principal) commit a crime. Unlike an accessory, an accomplice is usually present when the crime is committed. An accomplice is guilty of the same offense and usually receives the same sentence as the principal. For instance, the driver of the getaway car for a burglary is an accomplice and will be guilty of the burglary even though he may not have entered the building.

In criminal cases, a group that decides whether there is enough evidence to justify an indictment (formal charges) and a trial. A grand jury indictment is the first step, after arrest, in any formal prosecution of a felony.