The legal defence of ‘insanity’ states that the defendant is not capable of committing a crime as the individual is not aware of the nature or the quality of the act he has committed. Insanity is establishing that the mens rae (guilty mind) was in the individual’s control and if the act was his intention at the time of the offence and not the trial. It is only available as a defence in a murder charge.
Using the defence of insanity often increases the cost and length of a trial. Defence attorneys need to obtain experts that are able to spend time with the defendant in order to evaluate their past medical records and potentially give their testimony twice. Attorneys may not have the time or the resources to obtain past medical records to analyse whether the defendant will be a successful candidate for the use of insanity as a legal defence (Tindula, 2016).
Insanity, however, is now rarely used as a defence for a number of reasons. When it has been used in trials, it is rarely successful. A study by the US National Institute of Mental Health in eight US states found that the defence was filed in less than 1 per cent of all felony cases. Of those cases where the defence is successful in a small proportion of the cases.
In those rare cases when the insanity defence is successful, the defendant is admitted to a mental institute or a psychiatric hospital. The institution specializes in the treatment of serious mental disorders, such as severe depression, schizophrenia, and bipolar disorder. The aim of treatment is to rehabilitate an individual to return to society. The disadvantage of admitting a defendant into a psychiatric hospital is that it is much more restrictive than a general prison, as well as there is the possibility that the defendant will be held indefinitely.
The diminished responsibility defence has caused the insanity defence to be used even less. The legislation (the Coroners and Justice Act 2009), introduced in the Homicide Act 1957, states that individuals who kill another or are a part of it cannot be convicted of murder if the defendant was suffering from an abnormal mental functioning that’s caused by a recognised medical condition, making them unable to form rational judgements or exercise self-control. It explains the defendant’s acts or omissions that contributed to the killing.
In general, all of the above explains why insanity as a legal defence is now rarely used.