One of the strangest defences that has been used in criminal trials is that the accused was asleep or sleepwalking when they committed the offence.
Mens rea in the context of sleepwalking
The legal term mens rea refers to criminal intent, requiring a person to have awareness or knowledge that they are doing wrong in order to be convicted of a crime.
There have been cases where the defence has successfully argued that the accused was not in control of their actions at the time of the offence because they suffered from automatism, a term to describe body movements that are not consciously controlled, like breathing or sleepwalking.
In NSW a person can be found not guilty by reason of mental illness, where a special verdict of "act proven but not criminally responsible" applies. (Please see Section 32 Mental Health Act provisions replaced by new legislation in NSW.)
This verdict is applied to a defendant who is found to have a defect of reason caused by a disease of the mind, due to the fact that the defendant did not know the nature and quality of their act, and they did not know it was wrong.
This defence comes under the NSW Mental Health and Cognitive Impairment Forensic Provisions Act 2020.
In such cases the defendant can be detained as a forensic patient until their treatment and rehabilitation has been deemed adequate for their release into the community.
Committing illegal acts while sleepwalking or asleep
But doing illegal acts while asleep is different. It's called parasomnia, a sleep disorder that causes abnormal behaviour while sleeping.
It can include sleepwalking, talking and even sexsomnia - performing sexual acts while asleep. This condition is recognised in medical science. (Please see Sexsomnia - Excusable or Just Insane, Criminal Law Journal, 2015.)
Studies have found two to four per cent of adults sleepwalk, but sexsomnia is more rare.
Courts are very cautious when the accused claims to have no recollection of the offence. In cases where the defence of parasomnia has succeeded, the person has had to prove a history of parasomnia, and that they did nothing to indicate they were conscious while committing the offence.
Recent cases involving the sleepwalking defence
In a recent case in NSW, a man who sexually assaulted his underage daughter who was sharing his bed was found not guilty, because it was determined he was asleep at the time. He had a history of sexsomnia, and the judge said the prosecution had not proved he knew what he was doing at the time.
The court found sexsomnia was not a mental health impairment. (Please see NSW father and former school principal acquitted over sexual acts towards his daughter because he has 'sexsomnia'.)
In Scotland in 2020 a man was acquitted of several rape charges after a jury accepted he was unaware he was having sex because he was asleep. (Please see Rape accused who claimed 'sexsomnia' walks free from court.)
Sleepwalking has been used as a defence in other criminal cases. (Please see Not guilty Your Honour, I was sleepwalking when I did it.)
For more information please see When does the defence of mental health impairment apply?
Molly Hayter
Criminal law
Stacks Law Firm
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