Manslaughter by dangerous act, or by an omission to perform a legal duty, was considered by the High Court of Australia in Burns v The Queen  HCA 35 (14 September 2012). The death occurred after consumption of methadone, and the defendant (appellant) could have been liable for supplying the drug, for administering the drug, or for failing to render assistance to the victim in circumstances which gave rise to a duty of care. It was not possible to say why the jury had convicted the defendant. In the High Court the Crown conceded that the defendant could not be liable on the basis of supply of the drug. The Court unanimously held there was no basis in the facts for conviction for breach of a duty of care, and the majority (Heydon J dissenting) held that the facts did not exclude the possibility that the victim administered the drug to himself. The conviction was quashed and an acquittal entered.
The case is of interest for its illustration of the difference between moral and legal duties. While most people might think that a person who supplied an unlawful and dangerous drug to another owed a duty of care to that person to do what was reasonable in the interests of safety, there are difficulties in establishing a legal duty to do the same.
French CJ referred  to the "taxonomy" of the duties of care that may support a charge of manslaughter in cases like this: where a statute imposes a duty, where the duty arises from a certain status relationship, where the duty arises from contract, and where one person voluntarily assumes the care of another, secluding that other and preventing third persons from rendering aid. There may also be a duty of care where the defendant has caused a sequence of events which gave rise to a risk of injury.
Here there was  no statutory duty, no status relationship, no contract. On the facts the defendant had not assumed responsibility for care of the victim and had not secluded him so as to prevent others rendering assistance. As to creating a causative sequence of events giving rise to risk of injury, on the facts it was possible that the victim had injected himself with the drug  and he may even have rebuffed a suggestion that an ambulance should be called .
The joint judgment of Gummow, Hayne, Crennan, Kiefel and Bell JJ pointed  to difficulties with the proposition that those who unlawfully supply dangerous drugs have a duty to people they supply. What would discharge the duty of care? Supplying clean needles and syringes? Supplying information about levels of safe use? Ordinarily the supplier will have no control over how the recipient uses the drug. Is the duty (as was accepted in the appeal court below) confined to use of the drug in the supplier's presence? This, said the joint judgment, looks like imposing a duty because "it is an affront to morality that the supplier of a prohibited drug should not bear responsibility for the callous disregard for the life of the drug user." The absence of control counted against the imposition of a duty of care, and 
"... courts must be circumspect in identifying categories of relations that give rise to a previously unrecognised legal obligation to act [footnote: See, eg, R v Sinclair, Johnson and Smith unreported, England and Wales Court of Appeal (Criminal Division), 21 August 1998; B Hogan, "Omissions and the duty myth", in Smith (ed), Criminal Law: Essays in Honour of J C Smith, (1987) 85 at 87]."
So it was a matter for the legislature, not the courts, to develop the law on the liability of drug suppliers for harm to users (, Heydon J agreeing at ).
I should add that there is a useful discussion of liability for omissions by Andrew Ashworth QC, "Public Duties and Criminal Omissions: Some Unresolved Questions", available at the Association of Commonwealth Criminal Lawyers website. For legislative developments in New Zealand, see Crimes Act 1961, s 150A and the sections referred to therein.
Another decision of the High Court of Australia touching on the scope of criminal responsibility was delivered the same day: Likiardopoulos v The Queen  HCA 37 (14 September 2012). It is noteworthy for these points:
- French CJ was careful to distance himself from any (obiter) suggestion that the decision to prosecute is never reviewable.
- A person can be a secondary party to a greater offence even though the principal offender was convicted of a lesser offence. A lesser conviction does not of itself provide a shield for another person. If the prosecution can show that the principal did commit the greater offence, the defendant could be a party to that. The principal is not in jeopardy of conviction for the greater offence.
- The charging of the defendant as a secondary party to the commission of a more serious offence than that for which the principal was convicted does not of itself give rise to abuse of process or unfairness, especially where, as here, when the plea to the lesser offence was accepted there was insufficient evidence to charge the principal with the greater offence. The moral culpability of the secondary offender was, here, greater than that of the principal(s) in view of his being much older [joint judgment, 39].
- A revision of the law of complicity could result in too great a change – retrospective and adverse to the interests of defendants - for the courts to introduce and should be left to the legislature (Heydon J agreeing, ). The limit of secondary liability is set by the offence actually committed.
This last point was a response to the prosecution submission that liability of all secondary parties should be determined by their mens rea. That would mean that if the secondary party had the mens rea for murder, but murder could not be proved against the principal, the secondary party would be guilty of murder. The difference from this case is that the prosecution would not need to establish mens rea on the part of the principal offender. That would mean that even if the evidence was no stronger than it had been against the principal party when the plea to the lesser charge was accepted, the secondary party could still be convicted of murder. Should the secondary offender benefit from a fortuitous lack of evidence in relation to the principal offender, or should the same requirements of actus reus and mens rea apply to both principals and secondary parties? To what extent should the maxim actus non facit reum nisi mens sit rea apply – should the secondary party's guilty mind make the principal's act guilty in relation to the secondary party? Currently the law says there is only an actus reus if the principal has mens rea.