The crime of conspiracy is charged regularly in state and federal courts throughout the United States. This crime consists in an agreement by two or more individuals to commit an additional crime. The conspiracy charge is widely used in a number of different areas, particularly with respect to white-collar crimes and narcotics offenses. The prosecution views the crime of conspiracy as advantageous because it allows, in a single trial, for the prosecution of all conspirators wherever they are located, and it allows the government to prosecute the case in any city in which any act in furtherance of the agreement took place. In addition, statements made by any conspirator are allowed to be used against all other conspirators, and each conspirator can be found criminally responsible for other conspirators' crimes found to be in furtherance of the agreement.
Three major constitutional questions have arisen in conspiracy trials in the United States. The first deals with the double jeopardy clause of the Fifth Amendment, which provides in part, "nor shall any person be subject for the same offense to be twice put in jeopardy of life or limb." Most judges have concluded that the purpose of the double jeopardy clause was to ensure that a person could not be charged more than once for the same offense in the same jurisdiction. Individuals who are prosecuted for the conspiracy offense contend that if they are also charged with the crime that was the subject of the agreement (for example, bank robbery), their double jeopardy rights have been violated. The courts have consistently rejected this claim, however, holding that conspiracy (the agreement to commit bank robbery) and the crime (the actual bank robbery) are separate offenses. Hence, the defendant can receive separate punishment for each without the double jeopardy clause being violated.
Defendants also contend that being charged with conspiracies in two different courts violates their double jeopardy rights. For instance, conspiracy to rob a bank may be a violation of both state and federal law. It is a violation of state law because robbing any institution within the state is a crime. It is a violation of federal law because the bank may be a federally insured institution. Under the principle of "dual sovereignties" the Supreme Court has concluded that separate prosecutions and separate penalties for a federal conspiracy and a state conspiracy do not violate the double jeopardy clause, because such prosecutions are not multiple trials for the same offense by the same jurisdiction.
An additional constitutional issue is raised when defendants are charged with conspiring not to commit a crime but to commit acts that are "injurious to the public health or morals." These cases usually involve situations in which a particular form of behavior, such as charging usurious interest rates, is not itself criminal, but the defendant is charged with conspiring to commit that act. The Supreme Court in Musser v. Utah (1948) cast considerable doubt on the constitutionality of these prosecutions. The chief argument here is that such conspiracy prosecutions violate the due process clause of both the Fifth Amendment and fourteenth amendment because the phrase "acts injurious to the public health or morals" is so vague as to give insufficient guidance to citizens. As a consequence of the Musser decision, few prosecutions have been based upon this rather open-ended charge; instead, the government typically contends that the defendants have conspired to commit a particular crime and that crime is then set forth in some detail.
The third constitutional issue is perhaps the most famous and controversial, involving free speech implications under the first amendment. The problem surfaces when the defendants are charged with agreeing to advocate activities challenging the government. In such situations, the question is whether the agreement can be viewed as purely criminal behavior or whether, under the First Amendment, the behavior is protected speech. The most important Supreme Court case in the area is yates v. united states (1956). There the defendants were mid-level officials of the Communist party charged with conspiring to advocate the overthrow of the government of the United States by force and violence. In construing the Smith Act, the Court concluded that the prosecution, to succeed, must show an agreement to engage in unlawful action and a specific intent by each conspirator to engage in that action. If, however, the charge against the defendants were based upon their agreement to advocate the abstract principle of forcible overthrow of the government, that agreement would not violate the statute, even if such advocacy promoted violent activity.
Marcus, Paul 1991 The Prosecution and Defense of Criminal Conspiracy Cases. New York: Matthew Bender.