The Prosecutor relied on Osland v R (1998) 159 ALR 170 and the Court of Criminal Appeal New South Wales in Tangye . In Osland, Gaudron and Gummow JJ held at [72] - [75]:
However, there is a third category where a person was not only present at the scene with the person who committed the acts alleged to constitute the crime but was there by reason of a pre-concert or agreement with that person to commit the crime. In that category, the liability of each person present as the result of the concert is not derivative but primary. He or she is a principal in the first degree. In that category each of the persons acting in concert is equally responsible for the acts of the other or others. The general principle was clearly stated in R v Lowery and King (No 2) by Smith J who directed the jury in the following terms:
"The law says that if two or more persons reach an understanding or arrangement that together they will commit a crime and then, while that understanding or arrangement is still on foot and has not been called off, they are both present at the scene of the crime and one or other of them does, or they do between them, in accordance with their understanding or arrangement, all the things that are necessary to constitute the crime, they are all equally guilty of that crime regardless of what part each played in its commission. In such cases they are said to have been acting in concert in committing the crime."
In that case, his Honour directed the jury that "they are all equally guilty of that crime". But as subsequent cases show, and as principle requires, the correct statement is that they are all equally liable for the acts that constitute the actus reus of the crime. The principle is accurately stated by Brett, Waller and Williams in the 8th edition of their work on Criminal Law:
"[E]ven if only one participant performed the acts constituting the crime, each will be guilty as principals in the first degree if the acts were performed in the presence of all and pursuant to a preconceived plan. In this case, the parties are said to be acting in concert." (emphasis added)
So far as is presently relevant, these principles were accurately and more fully stated by the New South Wales Court of Criminal Appeal in Tangye. The Court said:
"(1) The law is that, where two or more persons carry out a joint criminal enterprise, each is responsible for the acts of the other or others in carrying out that enterprise. The Crown must establish both the existence of that joint criminal enterprise and the participation in it by the accused.
(2) A joint criminal enterprise exists where two or more persons reach an understanding or arrangement amounting to an agreement between them that they will commit a crime. The understanding or arrangement need not be express, and its existence may be inferred from all the circumstances. It need not have been reached at any time before the crime is committed. The circumstances in which two or more persons are participating together in the commission of a particular crime may themselves establish an unspoken understanding or arrangement amounting to an agreement formed between them then and there to commit that crime.
(3) A person participates in that joint criminal enterprise either by committing the agreed crime itself or simply by being present at the time when the crime is committed". (emphasis added)
In accordance with the New South Wales practice, the Court referred to "carrying out a criminal enterprise" rather than acting in concert. The principles, however, are the same.
As a result, a person may be found guilty of murder although he or she did not commit the acts which physically caused the death of the victim and the person who did is found guilty only of manslaughter. In R v Howe, all their Lordships were of the opinion that R v Richards, which had held that the person who did not perform the acts could not be guilty of a more serious charge than the actual perpetrator, was wrongly decided. Lord Mackay said:
"[W]here a person has been killed and that result is the result intended by another participant, the mere fact that the actual killer may be convicted only of the reduced charge of manslaughter for some reason special to himself does not, in my opinion in any way, result in a compulsory reduction for the other participant."
This statement is conclusive in England, at all events, in showing that it is the acts, and not the crime, of the actual perpetrator which are attributed to the person acting in concert. If the latter person has the relevant mens rea, he or she is guilty of the principal offence because the actus reus is attributed to him or her by reason of the agreement and presence at the scene. It is irrelevant that the actual perpetrator cannot be convicted of that crime because he or she has a defence such as lack of mens rea, self-defence, provocation, duress or insanity. [footnotes omitted]