Delaney v R [2025] NSWCCA 76

Delaney v R [2025] NSWCCA 76 · Read the judgment on AustLII

Catchwords: Mental health impairment – Drug use – Onus of proof where dispute about mental health impairment

The Court of Criminal Appeal has held that for the purposes of the definition of ‘mental health impairment’, the mere presence or absence of drug use at around the time is not decisive. The real question is whether any mental health impairment is caused solely by whatever drugs are present in the accused’s system. To the extent that the accused raises a mental health impairment, they bear the onus of establishing that aspect of the case. But if the Crown disputes the diagnosis on the basis it was caused solely by the ingestion of drugs or the existence of a substance use disorder, then the onus is on the Crown to prove the exception.

One afternoon the applicant had an entirely normal encounter with his sister and his cousin. Tragically, later that same afternoon he killed his sister with a hammer before wrapping her body in a blanket and placing an armchair over her body. He absconded, spending the next few days living in numerous locations, taking drugs, and transferring money from the deceased’s bank account into his own, before voluntarily admitting himself into Cumberland Hospital in connection with his drug use. The deceased’s body was found the day after he admitted himself to hospital, and he was charged with murder. His lawyers engaged a forensic psychiatrist on the question of whether the applicant had open to him the defence of mental health impairment – what practitioners might know in the vernacular as ‘the mental illness defence’, or by the more outdated term ‘insanity defence’. The psychiatrist diagnosed a mental health impairment (schizophrenia), but opined that the defence was not available because acute intoxication could not be excluded as ‘the most important factor’ in the offending. The Crown’s expert came to a similar conclusion. The applicant was advised that the defence of mental health impairment was not available and so, ostensibly having no defence, he chose to plead guilty. He was sentenced to imprisonment for 21 years, with a non-parole period of 15 years and 9 months. He sought leave to appeal against his conviction upon the ground that the expert opinion and advice were mistaken about the definition of ‘mental health impairment’ in s 4 of the Mental Health and Cognitive Impairment Forensic Provisions Act 2020 (‘MHCIFP Act’).

Section 4 of the MHCIFP Act sets out the definition of ‘mental health impairment’. Section 4(3) provides that a person does not have a mental health impairment for the purposes of the Act if the person’s impairment is ‘caused solely by’ the temporary effect of ingesting a substance, or a substance use disorder.

The Court (Davies J, with whom Harrison CJ at CL and Weinstein J agreed) observed that the test in MHCIFP Act s 4(3) is whether the relevant impairment was ‘caused solely by’ drug ingestion and cannot be equated to a ‘but for test’ where it would be sufficient to prove that but for the ingestion of drugs the psychosis would not have occurred (at [66]). In the present case, the two psychiatrists struggled with the fact that on top of the mental health impairment they considered that the applicant was acutely intoxicated by substances at the time of the killing. As a matter of law, it was not a question of not being able to exclude drug ingestion but rather whether that was the sole cause of the impairment (at [67]). Those advising the applicant operated on the basis that the applicant would have to prove that he was not taking drugs, but this advice did not engage with the ‘caused solely by’ test in s 4(3). Wherever the onus lay in relation to s 4(3), the applicant did not have to prove that he was not taking drugs at the time, nor did he have to exclude the effect of drug consumption as a contributing factor. The jury only had to be satisfied on all the evidence that the applicant’s impairment was not caused solely by (relevantly) the temporary effect of ingesting the drugs. The question was whether the applicant had a mental health impairment, and if so whether that mental health impairment fulfilled the criteria for the defence set out in s 28 of the MHCIFP Act. But the advice given to the applicant was that, in effect, he did not get to first base to put those matters to the jury. The advice given to the applicant was wrong (at [71]-[72]).

Although it was not ultimately necessary in order to decide the appeal, the Court also considered the question of who bore the onus of proof in respect of s 4 of the MHCIFP Act. If the issue of a mental health impairment is raised by an accused, the onus of proof of demonstrating the existence of the impairment lies on the accused (at [74]). However, s 4(3) provides an exception or a qualification for what is contained in s 4(1) (at [82]). The question of who bears the onus under s 4(3) only arises if an issue is raised suggesting that the accused’s impairment is caused solely by the matters in that sub-section. If the accused asserts only that they suffer from a mental health impairment, and the Crown seeks to show that the accused does not have a mental health impairment (whether for the purposes of the mental health impairment defence or otherwise), then the onus of proof is on the Crown to prove the exception that it has raised. There is no onus on the accused under s 4(3), even in circumstances where, on their own case, a substance was ingested, or a substance use disorder is raised on the evidence. That is because unless it is shown that the impairment was caused solely by the ingesting of the substance or the substance use disorder, the accused will not be precluded from relying on a mental health impairment (at [88]-[89]).

Given the overlap of mental illness and drug use – including the fact that causation often goes both ways – this decision will be important to bring to the attention of forensic psychiatrists briefed by practitioners. Notably, this decision applies just as much in Local Court matters as in higher courts, and because it goes to the heart of the definition of ‘mental health impairment’ its importance is not only limited to cases where a full defence is being investigated.