Criminal Law & Procedure – Lecture 2 (of 4): Substantive Criminal Law—Defenses and Introduction to Procedure

Summary of Criminal Procedure – Day 2

Introduction

Day 2 covers criminal defenses and an introduction to criminal procedure, focusing on legal justifications and constitutional protections under the Fourth Amendment.

Key Topics:

Defenses to Crimes: Insanity, infancy, intoxication, self-defense, duress, necessity, and entrapment.

Fourth Amendment: Search & seizure rules, warrant requirements, and exceptions.

Exclusionary Rule: Preventing use of illegally obtained evidence in court.

I. Defenses to Crimes

Criminal defenses fall into two categories: capacity defenses and justification/excuse defenses.

A. Capacity Defenses

Insanity:

Defendant lacked mental capacity to understand wrongdoing.

Tests: M’Naghten Rule, Irresistible Impulse Test, Durham Rule, MPC Standard.

Infancy:

Juveniles may not be held criminally responsible (common law: under age 7 presumed incapable).

Intoxication:

Voluntary intoxication: Not a defense unless it negates specific intent crimes.

Involuntary intoxication: Can be a defense if it causes loss of control or awareness.

B. Justification & Excuse Defenses

Self-Defense:

Use of force must be proportional and necessary.

Deadly force allowed if defendant faces imminent threat of death or serious harm.

Defense of Others & Property:

Same rules as self-defense, but no deadly force to protect property.

Duress:

Defendant coerced into committing a crime under threat of death or serious harm.

Not a defense for homicide.

Necessity:

Defendant committed a crime to prevent a greater harm (e.g., breaking into a cabin during a blizzard).

Entrapment:

Law enforcement induced crime that defendant was not predisposed to commit.

II. Introduction to Criminal Procedure

The Fourth Amendment protects against unreasonable searches and seizures by law enforcement.

A. Probable Cause & Warrants

Probable cause: Reasonable belief that a crime has been committed.

Warrant requirements: Issued by a neutral judge, based on sworn affidavit, specifying place and items to be searched.

Arrests require probable cause, but warrants are not always needed if arrest occurs in public.

B. Warrant Exceptions

Some searches do not require a warrant due to public safety concerns or exigent circumstances:

Search Incident to Arrest – Limited search of arrestee and immediate surroundings.

Exigent Circumstances – Immediate threat to safety or evidence destruction.

Consent Searches – Voluntary consent waives Fourth Amendment rights.

Automobile Exception – Cars have reduced privacy, allowing searches with probable cause.

Plain View Doctrine – Officers can seize evidence in plain sight if lawfully present.

Stop and Frisk (Terry Stop) – Officers may briefly detain and pat down suspects if there is reasonable suspicion of criminal activity.

C. The Exclusionary Rule & Fruit of the Poisonous Tree

Illegally obtained evidence is inadmissible in court (Mapp v. Ohio (1961)).

Exceptions:

Good Faith Exception: Police relied on a warrant later found invalid.

Inevitable Discovery: Evidence would have been found legally.

Independent Source: Evidence came from separate, legal investigation.

Conclusion

Day 2 covered criminal defenses and the Fourth Amendment’s search and seizure protections. These legal principles help determine when a defendant is legally excused and when law enforcement actions violate constitutional rights. Next time we will continue with Fifth and Sixth Amendment protections and trial procedures.