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In criminal law, a conspiracy is an agreement between two or more persons to commit a crime at some time in the future. Criminal law in some countries or for some conspiracies may require that at least one overt act must also have been undertaken in furtherance of that agreement, to constitute an offense. There is no limit on the number participating in the conspiracy and, in most countries, no requirement that any steps have been taken to put the plan into effect (compare attempts which require proximity to the full offence). For the purposes of concurrence, the actus reus is a continuing one and parties may join the plot later and incur joint liability and conspiracy can be charged where the co-conspirators have been acquitted or cannot be traced. Finally, repentance by one or more parties does not affect liability but may reduce their sentence.
England and Wales 
Common law offence 
At common law, the crime of conspiracy was capable of infinite growth, able to accommodate any new situation and to criminalize it if the level of threat to society was sufficiently great. The courts were therefore acting in the role of the legislature to create new offences and, following the Law Commission Report No. 76 on Conspiracy and Criminal Law Reform, the Criminal Law Act 1977 produced a statutory offence and abolished all the common law varieties of conspiracy, except two:
Conspiracy to defraud 
|This section requires expansion. (May 2013)|
Conspiracy to corrupt public morals or to outrage public decency 
Conspiracy to corrupt public morals is an offence under the common law of England and Wales.
Conspiracy to outrage public decency is an offence under the common law of England and Wales.
Section 5(1) of the Criminal Law Act 1977 does not affect the common law offence of conspiracy if, and in so far as, it can be committed by entering into an agreement to engage in conduct which tends to corrupt public morals, or which outrages public decency, but which does not amount to or involve the commission of an offence if carried out by a single person otherwise than in pursuance of an agreement.
Jonathan Herring said that conspiracy to "corrupt public morals" has no definitive case law, that it is unknown whether or not it is a substantive offence, and that it is unlikely that conspirators will be prosecuted for this offence.
These two offences cover situations where, for example, a publisher encourages immoral behavior through explicit content in a magazine or periodical. But, in R v Rowley, the defendant left notes in public places over a period of three weeks offering money and presents to boys with the intention of luring them for immoral purposes, but there was nothing lewd, obscene or disgusting in the notes. The judge ruled that the jury was entitled to look at the purpose behind the notes in deciding whether they were lewd or disgusting. On appeal against conviction, it was held that an act outraging public decency required a deliberate act which was in itself lewd, obscene or disgusting, so Rowley’s motive in leaving the notes was irrelevant and, since there was nothing in the notes themselves capable of outraging public decency, the conviction was quashed.
Statutory offence 
This offence was created as a result of the Law Commission's recommendations in their Report, Conspiracy and Criminal Law Reform, 1976, Law Com No 76. This was part of the Commission's programme of codification of the criminal law. The eventual aim was to abolish all the remaining common law offences and replace them, where appropriate, with offences precisely defined by statute. The common law offences were seen as unacceptably vague and open to development by the courts in ways which might offend the principle of certainty. There was an additional problem that it could be a criminal conspiracy at common law to engage in conduct which was not in itself a criminal offence: see Law Com No 76, para 1.7. This was a major mischief at which the 1977 Act was aimed, although it retained (as a temporary measure) the convenient concept of a common law conspiracy to defraud: see Law Com No 76, paras 1.9 and 1.16. Henceforward it would only be an offence to agree to engage in a course of conduct which was itself a criminal offence.
Section 1(1) of the Criminal Law Act 1977 provides:
- "...if a person agrees with any other person or persons that a course of conduct shall be pursued which, if the agreement is carried out in accordance with their intentions, either -
- (a) will necessarily amount to or involve the commission of any offence or offences by one or more of the parties to the agreement, or
- (b) would do so but for the existence of facts which render the commission of the offence or any of the offences impossible, [added by S.5 Criminal Attempts Act 1981]
- he is guilty of conspiracy to commit the offence or offences in question."
Section 1(1A) bans conspiracies part of which occurred in England and Wales to commit an "act or other event constitutes an offence under the law in force in that country or territory." Many conditions apply including prosecutions need consent from the Attorney General.
- Under section 2(1) the intended victim of the offence can not be guilty of conspiracy.
- Under section 2(2) there can be no conspiracy where the only other person(s) to the agreement are:
Elements of the offence 
There must be a real agreement with the parties having agreed all the major details of the "crime" or "crimes" (not including other inchoate offences) to be committed within the territorial jurisdiction of the court, and the parties must "intend" or "know" the facts which make the conduct criminal even where the full offence is strict. Thus, the mens rea of conspiracy is a completely separate issue from the mens rea required of the substantive crime; where the issue of corruption in public office was complicated by the presence of the presumption of corruption in section 2 of the Prevention of Corruption Act 1916 unless the contrary is proved in respect of payments to persons in public employment (a provision that probably breaches the human rights requirement as to a presumption of innocence).
The so-called Wharton's rule (also known as "Concert of Action Rule") regarding conspiracies is relatively simple: Unless the statute specifies otherwise, when two people are required to commit a crime, such as gambling or prostitution, there can be no charge of conspiracy where only two people are involved. The reasoning behind this rule, which has been enacted in many states, is that conspiracies, by their very nature, bring together individuals with different resources and abilities. This group action is dangerous. However, where there are only two people involved in a crime that requires two people to commit it, there is no concerted group action. To prosecute gambling or prostitution as a conspiracy, most states require that more than two people be involved.
Things said or done by one conspirator 
Lord Steyn in R v Hayter said:
The rule about confessions is subject to exceptions. Keane, The Modern Law of Evidence 5th ed., (2000) p 385–386, explains:
- "In two exceptional situations, a confession may be admitted not only as evidence against its maker but also as evidence against a co-accused implicated thereby. The first is where the co-accused by his words or conduct accepts the truth of the statement so as to make all or part of it a confession statement of his own. The second exception, which is perhaps best understood in terms of implied agency, applies in the case of conspiracy: statements (or acts) of one conspirator which the jury is satisfied were said (or done) in the execution or furtherance of the common design are admissible in evidence against another conspirator, even though he was not present at the time, to prove the nature and scope of the conspiracy, provided that there is some independent evidence to show the existence of the conspiracy and that the other conspirator was a party to it.
Conspiracy to trespass 
|This section requires expansion. (May 2013)|
See Kamara v Director of Public Prosecutions
Conspiracy to effect a public mischief 
In Withers v Director of Public Prosecutions, the House of Lords unanimously held that conspiracy to effect a public mischief was not a separate and distinct class of criminal conspiracy. This overruled earlier decisions to the contrary effect.
The Law Commission published a consultation paper on this subject in 1975.
Conspiracy to murder 
Northern Ireland 
Common law offence 
Statutory offence 
See Part IV of the Criminal Attempts and Conspiracy (Northern Ireland) Order 1983 (S.I. 1983/1120 (N.I. 13)).
United States 
Conspiracy has been defined in the US as an agreement of two or more people to commit a crime, or to accomplish a legal end through illegal actions. For example, planning to rob a bank (an illegal act) to raise money for charity (a legal end) remains a criminal conspiracy because the parties agreed to use illegal means to accomplish the end goal. A conspiracy does not need to have been planned in secret to meet the definition of the crime. One legal dictionary, law.com, provides this useful example on the application of conspiracy law to an everyday sales transaction tainted by corruption. It shows how the law can handle both the criminal and the civil need for justice.
[A] scheme by a group of salesmen to sell used automobiles as new, could be prosecuted as a crime of fraud and conspiracy, and also allow a purchaser of an auto to sue for damages [in civil court] for the fraud and conspiracy.
Conspiracy law usually does not require proof of specific intent by the defendants to injure any specific person to establish an illegal agreement. Instead, usually the law only requires the conspirators have agreed to engage in a certain illegal act. This is sometimes described as a "general intent" to violate the law.
Under most U.S. laws, for a person to be convicted of conspiracy not only must he or she agree to commit a crime, but at least one of the conspirators must commit an overt act (the actus reus) in furtherance of the crime. However, in United States v. Shabani the U.S. Supreme Court ruled that this "overt act" element is not required under the federal drug conspiracy statute, 21 U.S.C. section 846.
The conspirators can be guilty even if they do not know the identity of the other members of the conspiracy. See United States v. Monroe, 73 F.3d 129 (7th Cir. 1995), aff'd., 124 F.3d 206 (7th Cir. 1997).
California criminal law is somewhat representative of other jurisdictions. A punishable conspiracy exists when at least two people form an agreement to commit a crime, and at least one of them does some act in furtherance to committing the crime. Each person is punishable in the same manner and to the same extent as is provided for the punishment of the crime itself. 
One example of this is The Han Twins Murder Conspiracy case, where one twin sister attempted to hire two youths to have her twin sister killed.
One important feature of a conspiracy charge is that it relieves prosecutors of the need to prove the particular roles of conspirators. If two persons plot to kill another (and this can be proven), and the victim is indeed killed as a result of the actions of either conspirator, it is not necessary to prove with specificity which of the conspirators actually pulled the trigger. (Otherwise, both conspirators could conceivably handle the gun—leaving two sets of fingerprints—and then demand acquittals for both, based on the fact that the prosecutor would be unable to prove beyond a reasonable doubt, which of the two conspirators was the triggerman). A conspiracy conviction requires proof that a) the conspirators did indeed conspire to commit the crime, and b) the crime was committed by an individual involved in the conspiracy. Proof of which individual it was is usually not necessary.
It is also an option for prosecutors, when bringing conspiracy charges, to decline to indict all members of the conspiracy (though their existence may be mentioned in an indictment). Such unindicted co-conspirators are commonly found when the identities or whereabouts of members of a conspiracy are unknown; or when the prosecution is only concerned with a particular individual among the conspirators. This is common when the target of the indictment is an elected official or an organized crime leader; and the co-conspirators are persons of little or no public importance. More famously, President Richard Nixon was named as an unindicted co-conspirator by the Watergate special prosecutor, in an event leading up to his eventual resignation.
Conspiracy against rights 
International law 
Conspiracy law was used at the Nuremberg Trials for Nazi leadership who were charged with participating in a "conspiracy or common plan" to commit international crimes. This was controversial because conspiracy was not a part of the European civil law tradition. Nonetheless, the crime of conspiracy continued in international criminal justice, being incorporated into the international criminal laws against genocide.
It should however be noted, that of the Big Five, only the French Republic exclusively subscribed to the civil law; the USSR subscribed to the socialist law, the U.S. and the U.K. followed the common law; and the Republic of China did not have a cause of action at this particular proceeding. (In addition, it upheld both the civil and the customary law). In any event, the jurisdiction of the International Military Tribunal was unique and extraordinary at its time, being a court convened under the law of nations and the laws and customs of war, was the first of its sort in human history, found several defendants before it not guilty, and, of the guilty parties, it is certainly arguable that of the conspiracies plotted, many bore fruit.
See also 
- Report on Conspiracy and Criminal Law Reform  EWLC 76 (01 January 1976)
- Shaw v Director of Public Prosecutions  AC 220,  2 WLR 897,  2 All ER 446, 125 JP 437, 105 Sol Jo 421, 45 Cr App R 113, HL; Knuller (Publishing, Printing and Promotions) Ltd v Director of Public Prosecutions  AC 435,  3 WLR 143,  2 All ER 898, 136 JP 728, 116 Sol Jo 545, 56 Cr App R 633, HL
- Knuller (Publishing, Printing and Promotions) Ltd v Director of Public Prosecutions;;  AC 435,  3 WLR 143,  2 All ER 898, 136 JP 728, 116 Sol Jo 545, 56 Cr App R 633, HL (Lords Diplock and Reid dissenting)
- Criminal Law Act 1977, section 5(3)
- Herring, Jonathan (2008). Criminal Law: Text, Cases and Materials (3rd ed.). Oxford University Press. p. 812. ISBN 978-0-19-923432-5.
- R v Rowley,  4 All ER 649
- Attorney General ex parte Rockall  Crim LR 972
- Rockall, R (on the application of) v The Attorney General  EWHC B4 (Admin) (02 July 1999)
- R v Hayter  UKHL 6 (3 February 2005) at paragraph 25
- Kamara v Director of Public Prosecutions  AC 104,  3 WLR 198,  2 All ER 1242, 117 Sol Jo 581, 57 Cr App R 880, HL
- Withers v DPP  3 WLR 751, HL
- The Law Commission. Codification of the Criminal Law: Conspiracies to effect a public mischief and to commit a civil wrong. Working Paper No 63. 1975. para. 4 to 30
- Conspiracy Law & Legal Definition, USLegal, Inc.
- "Conspiracy" Defined & Explained, The 'Lectric Law Library
- Title 18, U.S.C., Section 241 - Conspiracy Against Rights
- Fichtelberg, Aaron, "Conspiracy and International Criminal Justice" (2006) Criminal Law Forum Vol 17, No. 2.