Criminal Law

Lesson 15: Insanity Defense

The insanity defense is a legal strategy where defendants argue they shouldn't be held criminally responsible due to mental illness. It's a subset of Defenses to Crimes.

It is important to distinguish between Mens Rea (the mental state of the defendant) and the insanity defense, which focuses specifically on the defendant's mental condition at the time of the crime.

Legal Standards for Insanity

Several legal standards have been developed to determine insanity. These include the M'Naghten Rule, the Irresistible Impulse Test, the Durham Rule, and the Model Penal Code standard. Below is a comparison of these standards:

M'Naghten Rule: This rule focuses on whether the defendant knew the nature and quality of the act or whether they knew it was wrong. Irresistible Impulse Test: This test considers whether the defendant was unable to control their actions or conform their conduct to the law. Durham Rule: This rule states that a defendant is not criminally responsible if the unlawful act was the product of mental illness. Model Penal Code: This standard combines aspects of the M'Naghten Rule and the Irresistible Impulse Test, stating that a defendant is not responsible if they lack substantial capacity to appreciate the criminality of their conduct or to conform their conduct to the law due to mental disease or defect.

Flowchart of the Insanity Defense Process

graph TD; A["Crime Committed"] --> B["Plea of Not Guilty by Reason of Insanity"]; B --> C["Psychiatric Evaluation"]; C --> D{{"Competent to Stand Trial?"}}; D -->|Yes| E["Insanity Defense Trial"]; D -->|No| F["Defendant Sent to Mental Institution"]; E --> G["Jury Decision"]; G -->|Not Guilty| H["Defendant Released"]; G -->|Guilty| I["Defendant Sent to Prison or Mental Institution"];

Case Studies

To understand the application of the insanity defense, here are some notable case studies:

John Hinckley Jr.: Attempted assassination of President Ronald Reagan. Hinckley was found not guilty by reason of insanity.
Andrea Yates: Drowned her five children. Yates was initially convicted of murder, but the conviction was overturned, and she was found not guilty by reason of insanity in a retrial.
The Insanity Defense: Multidisciplinary Views on Its History, Trends, and Controversies

Mathematical Representation of Responsibility

The concept of criminal responsibility can be mathematically represented as:

\[ \text{Responsibility} = \text{Mens Rea} \times \text{Actus Reus} \]

If a defendant is found to be insane, the Mens Rea component is considered to be zero, thus nullifying criminal responsibility.

Conclusion

The insanity defense is a complex and often controversial part of criminal law. It requires a thorough understanding of both legal and psychiatric principles. For more information on other defenses to crimes, consider reading Self-Defense and Duress. Also, check out The Insanity Defense: Multidisciplinary Views on Its History, Trends, and Controversies.