Background
Lucas Christian Delaney was charged with murdering his sister, Gabriella Delaney, at Cambridge Park in June 2020. On the agreed facts, Delaney repeatedly struck her in the head with a hammer, transferred money from her accounts, stayed elsewhere for several nights and was later admitted voluntarily to Cumberland Hospital. The Court was satisfied beyond reasonable doubt that he committed the physical acts constituting murder.
Delaney initially pleaded guilty and was sentenced in 2022 to 21 years’ imprisonment, with a non-parole period of 15 years and nine months. In 2025, the New South Wales Court of Criminal Appeal quashed the conviction, allowed him to withdraw the plea and remitted the case for retrial because the expert evidence and legal advice underlying the plea had misunderstood the statutory definition of mental health impairment.
Before the scheduled retrial, the prosecution and defence agreed that the proposed evidence established the defence of mental health impairment. The Supreme Court therefore conducted a hearing under s 31 of the Mental Health and Cognitive Impairment Forensic Provisions Act 2020 (NSW) to decide whether the evidence justified a special verdict of act proven but not criminally responsible.
The Court’s Holding
Dhanji J found on the balance of probabilities that, when Delaney killed his sister, he had schizophrenia or at least schizoaffective disorder and could not reason with a moderate degree of sense and composure about whether his act, as perceived by reasonable people, was wrong. Both psychiatric experts ultimately agreed that his impairment was not caused solely by temporary intoxication: his underlying psychotic illness or vulnerability was also causally involved.
Because the physical elements of murder were proved beyond reasonable doubt but the statutory mental-health defence was established, the Court returned the special verdict “act proven but not criminally responsible.” Delaney was ordered detained in a correctional facility or another place determined by the Mental Health Review Tribunal until released by due process of law, and he was referred to the Tribunal for ongoing review. The family’s victim impact statements were also ordered to be provided to the Tribunal.
Key Takeaways
- A special verdict under s 31 requires the Court—not merely the parties—to be satisfied that the evidence establishes the mental-health defence.
- Substance use does not exclude a mental health impairment unless the impairment was caused solely by temporary ingestion or by a substance use disorder.
- A finding of act proven but not criminally responsible avoids conviction and ordinary sentencing, but may result in indefinite forensic detention subject to Mental Health Review Tribunal supervision.
Why It Matters
The decision illustrates the distinction between intoxication triggering psychosis and intoxication being the sole cause of the relevant impairment. Even if drug ingestion was a necessary trigger, the statutory exclusion did not apply where a pre-existing psychotic illness or vulnerability also caused the condition.
It also demonstrates the procedural consequences of the special verdict: the Court still determines whether the charged acts were proved, while decisions about detention, placement and eventual release move into the forensic mental-health regime.