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Insanity Defence In Criminal Law

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Insanity Defence In Criminal Law

There are many criminal law defences which are used to try and explain why criminal liability is either mitigated or removed in any given criminal situation. Criminal responsibility refers to the notion that an individual be held responsible for his or her criminal actions which has created a particular scenario.

A defence of insanity in particular however is a difficult defence to argue. It considers a complex legal complex. If you think this is a path you will need to take in a criminal matter, you will likely require expert legal advice to see you through the process. Contact Jameson Law today for assistance with any criminal law matter.

What Is Mental Illness?

Mental illness describes a range of conditions which can range from mild to severe mental health conditions. Mental illness refers to a condition which affects the ability of an individual to make rational decisions, emotional decisions or affects their capacity to function fully.

Mental illness can create minimal impairment or severe impairment depending on the type of condition. For example, an anxiety disorder is likely to be less severe than bipolar disorder or schizophrenia due to the way that it affects both the brain and body. Mental health treatment for some conditions can be more effective than others.

An individual can have a diagnosed mental illness however but not be considered to have diminished mental capacity. The two do not go hand in hand. The mere existence of mental illness does not render a person incapable of being held responsible for their actions. It is still the burden of proof for the prosecution to prove beyond a reasonable doubt that the defendants conduct was legally wrong and they should not have diminished responsibility for their actions.

What Is An Insanity Defense?

An insanity defences works on the understanding that the individual lacks substantial capacity to be held responsible for their unlawful act or actions. This is on the basis that the person’s ability and mental state is impaired to such a degree that they are deemed to have little to no control over their actions.

Mental incompetence is difficult to prove because the threshold of medical evidence is high. The individual will need to be assessed by a psychiatrist and other treating medical professionals who specialize in mental disorders. A diminished capacity defense must always be backed up by medical evidence however this is only the first step. To prove insanity, a thorough psychological assessment is required. This is a long, often multi layered process.

Once mental competence is assessed, history is usually considered to see whether mental illness is a long standing issue. It is unusual for an insanity defense to be successful if there is no prior occurrence of mental health issues.

How Is An Insanity Defense Disproved?

Proving insanity is one thing but disproving insanity is just as important depending what side of the argument you are on. An insanity plea means that an “insane defendant” cannot present any arguments against their behaviour because their defence is that the defendant’s mental state was such at the time that they cannot be held responsible.

It is the role of the prosecution to prove that the criminal conduct would not have been committed by an ordinary person faced with the same situation and the same circumstances whether mentally ill or not.

A mental illness defence is largely reliant on psychiatric evidence following an assessment of the criminal defendant. If the prosecution are able to bring conflicting evidence on this point then they have a better chance to prove sanity instead. Even a temporary insanity defense must have compelling evidence to suggest that the defendant did not have substantial capacity at the time of the offence.


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