Conspiracy is a continuous crime. It extends over the period of the agreement and lasts as long as it is being performed. It remains a single conspiracy no matter who joins or leaves it, provided that at any one time there are at least two persons acting in combination to achieve the same criminal objective: R v Masters (1992) 26 NSWLR 450 at 458; R v Richards (1992) 26 NSWLR 450 at 458; Truong v The Queen (2004) 223 CLR 122 at [35]. Thus, acts and statements of alleged co-conspirators may be admissible against an accused (subject to the tests in Note 3 below) even if they were done or made after the accused was arrested: R v Louden (1995) 37 NSWLR 683.

In a joint trial for conspiracy, the summing up must deal separately with the case against each accused and the trial judge must separate the evidence properly relevant and admissible against each of them: R v Dougas [2021] NSWSC 682 at [78]; R v Cosgrove and Hunter (unrep, 15/08/88, NSWCCA).

Before the “co-conspirator rule” can operate to permit acts and statements of others, in the absence of a particular accused, to be evidence in the case against that accused, the trial judge must have determined (on the basis of other evidence admissible in the ordinary way against that accused) that there is prima facie reasonable evidence of participation of that accused in the alleged conspiracy. The jury is not to be told of the trial judge’s finding, and there need not be a formal judgment or ruling to that effect, but the trial judge must indicate that they are satisfied that there is such reasonable evidence of participation prior to the summing up. It will usually be prudent for the trial judge to discuss with counsel how the jury will be directed in relation to the evidence of acts or statements of co-conspirators: R v Masters.

If there is reasonable independent evidence of an accused’s participation, then acts or statements in their absence will be admissible against them to prove the existence of the conspiracy and the nature of it. If those acts or statements were done or made in furtherance of the conspiracy, then they will also be admissible on the issue of the accused’s participation in the alleged agreement. If, however, the Crown alleges that the accused joined the conspiracy after it had commenced, then acts done or statements made prior to their joining the alleged conspiracy are admissible only to prove the existence of the alleged agreement and the nature of it, but not to prove their participation, and the jury should be carefully instructed on the limited way that evidence can be used. See generally: Ahern v The Queen (1988) 165 CLR 87; R v Masters; R v Chai (1992) 27 NSWLR 153; R v Houlker (unrep, 19/03/93, NSWCCA); DPP (Cth) v Kola (2024) 279 CLR 104 at [44].

Section 57(2) of the Evidence Act 1995 provides that, if the relevance of evidence of an act done by a person depends on the court making a finding that the person and one or more other persons had, or were acting in furtherance of, a common purpose (whether to effect an unlawful conspiracy, or otherwise), the court may use the evidence itself in determining whether the common purpose existed. The admission of this evidence is an exception to the hearsay rule: Evidence Act, ss 59(1) and 60(1); DPP (Cth) v Kola at [44]. Where evidence is admitted on a provisional basis under s 57(2), even though its admissibility is in issue, and it transpires that there was no other evidence of common purpose involving the relevant accused, it will probably be necessary for the judge to exclude the evidence at a later stage.

Section 87(1)(c) of the Evidence Act provides that, for the purpose of determining whether a previous representation made by a person is also taken to be an admission by a party, the court is to admit the representation if it is reasonably open to find it was made by the person in furtherance of a common purpose (whether lawful or not) that the person had with the party or one or more persons including the party. Sections 57 and 87 assume the existence of the common law co-conspirators rule but remove the requirement that there be evidence extraneous to the representation to establish the common purpose: Macdonald v R [2023] NSWCCA 250 at [148]–[149].

It is open to the trial judge in the exercise of their discretion, even where it is found that there is reasonable evidence of participation against a particular accused, to exclude evidence of the acts and statements of others from consideration in the case against that accused (pursuant to s 135 or s 137 of the Evidence Act) and/or to limit the use to which the jury might put such evidence under s 136 of the Evidence Act.

A warning under s 165 of the Evidence Act may be appropriate, for example, in relation to the hearsay nature of evidence of the acts and statements of others in the absence of a particular accused which implicate that accused, particularly if the accused had no opportunity to cross-examine the makers as to the truth of their representations: R v Chai (decided under the common law).

The common law rule that a husband and wife cannot be found guilty of conspiring together has been abolished: Crimes Act 1900, s 580D.

The Criminal Procedure Act 1986, Sch 3, cl 21 applies to an indictment for conspiracy and provides that it is not necessary to state any overt act of conspiracy. No more than three counts against the same accused person may be inserted in one indictment: Sch 3, cl 21(4). An indictment can allege that the accused conspired “with an unknown person” as Sch 3, cl 21 does not abrogate the common law: R v Harrison (1995) 79 A Crim R 149.

As to conspiracy to defraud, the jury should be directed that this involves an agreement to use dishonest means to achieve an object, and an agreement to bring about a situation to deprive another person of money or property, or to imperil the other person’s rights or interests, knowing that they have no right to deprive that other person of money or property, or imperil that other person’s rights or interests. The summing up should identify the dishonest means relied upon by the Crown: Peters v The Queen (1998) 192 CLR 493 at [30]–[33]; [72], [83]; Spies v The Queen (2000) 201 CLR 603 [77]–[80]. See also Defraud — Intent to [5-5500].

Having regard to the definition of “supply” in s 3 of the Drug Misuse and Trafficking Act 1985, it is not open to the Crown to charge a conspiracy to supply a prohibited drug where the accused agreed with another to supply a prohibited drug to that other person: R v Chow (1987) 11 NSWLR 561; R v Challita (1988) 37 A Crim R 175 at 184 (both cases considered the identical definition of “supply” in the Poisons Act 1966, now the Poisons and Therapeutic Goods Act 1966). Nor does an expectation by a seller that the purchaser of a prohibited drug would on-sell it to others amount to an agreement to establish a conspiracy: R v Trudgeon (1988) 39 A Crim R 252. It is, however, open to the Crown to charge a conspiracy where the accused is alleged to have agreed with another or others to supply drugs to the public generally, or to a person, or persons not being conspirators with them: Tannous v The Queen (1989) 64 ALJR 141. Section 26 of the Drug Misuse and Trafficking Act provides that a person who conspires with another person or other persons to commit an offence under Div 2 is guilty of an offence.

An accused may be liable for conspiracies to do the factually impossible: R v El Azzi [2001] NSWCCA 397 at [34].