Home Society & Culture A Guide to Using the Insanity Defence in a Criminal Trial

A Guide to Using the Insanity Defence in a Criminal Trial

Reading Time: 2 minutes

The goal of any criminal defence lawyer is to help their client put together a strong defence. The stronger the defence is, the more likely it can sometimes be for a client to have their charges reduced or dropped altogether.

In some criminal trials, clients and their lawyers will attempt to use the insanity defence. Understanding this form of defence can be crucial for using it to your advantage.

What is an insanity defence? 

Many law firms, like Garland, Samuel & Loeb use the insanity defence when they don’t believe their clients were of sound mind when they committed a crime. It means that the defendant admits their criminal actions but isn’t culpable because they were experiencing a mental illness. 

This defence differs from others in that it’s an affirmative defence, not a partial defence. A partial defence aims to mitigate a defendant’s guilt by, for example, saying they were provoked. In contrast, an affirmative defence describes the introduction of evidence to negate criminal or civil liability, such as necessity, entrapment, self-defense, or insanity. 

How can you test for legal insanity? 

Anyone can say they have a mental illness like depression, anxiety, PTSD, or bipolar disorder. However, proving it in a court of law can be challenging. Most legal professionals use a variety of tests to establish cases of legal insanity, such as: 

  • Model Penal Code
  • Durham Standard
  • M’Naghten Rule
  • Irresistible Impulse Tests

The type of test a defendant undertakes can depend on their mental health disorder and its impact on their case. For example, you might use the M’Naghten Rule to prove that a defendant couldn’t distinguish right from wrong due to a disease of the mind. 

Can you be found legally insane everywhere? 

Laws differ from state to state. As a result, you can be found not guilty by reason of insanity in some states but not in others. Idaho, Kansas, Montana, and Utah have all abolished the insanity defence. Instead, some of these states allow a “guilty but insane” verdict. All other states rely on various mental health tests, such as modified versions of the M’Naghten Rule, the Model Penal Code, and the Durham Standard.

How do you prove insanity as a defence? 

If your lawyer has recommended that you plead insanity, you can get to work trying to prove it. This can involve a complete mental evaluation. Psychiatrists and psychologists can also be relied on to provide expert testimony. Their experience can shed light on what your state of mind might have been during your crime.

But a mental evaluation and expert testimonies are not certain ways to prove insanity. It’s ultimately up to a judge and jury to decide. They will review all available evidence to draw a conclusion. If you’ve been found not guilty by reason of insanity, you may receive treatment rather than punishment. As a result, you may stand a chance of rehabilitation. 

The insanity defence can be complex. Your lawyer may believe you were experiencing a mental illness at the time of your crime, but proving it can be challenging. The information above may prove helpful for understanding what can be involved in using insanity as a defence to see if it’s the right strategy for your unique situation.




Adam Mulligan, a psychology graduate from the University of Hertfordshire, has a keen interest in the fields of mental health, wellness, and lifestyle.

© Copyright 2014–2034 Psychreg Ltd