CRJU212

Week 3 Lecture

The Law and Criminal Investigations

All actions of investigators are governed by law, especially regarding the collection of evidence. The 4th, 5th, and 6th Amendments to the U.S. Constitution aim to protect individuals from unlawful searches and seizures, self-incrimination, and provide an attorney during legal proceedings.


It is important that investigators adhere to these legal constraints so that evidence can be admissible in a court of law to convict the accused. Investigators therefore, arrest and search according to certain requirements.


Due to the complexity of investigative work however, exceptions to the rules have been created over time as new issues arise.

Basic Legal Terminology

An arrest is when a person is taken into custody for the purpose of prosecution or interrogation.


An arrest warrant is a writ based on probable cause that is issued by a magistrate requiring the police to arrest a perpetrator (Garner, 2000).


An arrest warrant is required when:


  • The police must enter a home to make an arrest
  • The police seek to make an arrest in a third party’s home (Steagald v. U.S. 1981)


Exceptions to the requirement of an arrest warrant:

  • Exigent circumstances (Payton v. New York 1980)
  • Consent (Steagald v. U.S. 1981)


A search is when the government infringes upon a person’s reasonable expectation of privacy for the purpose of obtaining evidence (Katz v. U.S. 1967).


A search warrant is similar to an arrest warrant but instead indicates what is to be searched and the types of items that can be seized if found in the search.


The Rules and Admissibility of Evidence

  • All evidence must be relevant to the case or a fact of the case that is being questioned.
  • All evidence must be material or significant in determining the existence of a fact.
  • All evidence must be competent or valuable. Incompetent evidence is invalid and therefore inadmissible. Incompetent evidence falls into three categories:
  • Evidence that is wrongfully obtained like through an illegal search.
  • Statutory evidence, or any form of evidence that is prohibited by law, such as polygraph results.
  • Court-established rules like hearsay evidence.


All evidence must be necessary.


A chain of custody must be maintained. A chain of custody refers to the recorded security of physical evidence from the time of collection to its introduction in court.


The Search Warrant Requirement and Its Exceptions


Obtaining a search warrant through probable cause is the legal and valid way to conduct a search.


However there are exceptions to this rule:

  • Exigent circumstances, or emergency situations where evidence can be destroyed or people can get hurt if police do not act immediately are an exception.
  • Vehicles are an exception because they are mobile in nature and there are significant dangers for police in roadside encounters.


Reasonable suspicion is needed to stop a vehicle, order occupants out of the vehicle, and search occupants and the passenger compartment for weapons. Every other search of a vehicle however requires probable cause.


Other places and things not included in the 4th Amendment is an exception to the search warrant requirement. This category includes open fields and bank records.

  • The hot-pursuit exception applies when someone tries to avoid apprehension and the police follow to make an arrest and conduct a search because delaying could result in the loss of evidence or physical harm.
  • The search incident to arrest exception applies when the police arrest someone and conduct a search as a result of that arrest due to the threat of danger.
  • The stop and frisk exception applies when a search is needed for safety reasons, though an arrest may not be necessary.
  • The plain-view exception applies when evidence is observed during a police’s legal presence at that place.
  • The consent exception is the most commonly performed search for it is done without a warrant but with the consent of the person being searched. No probable cause or reasonable suspicion is necessary to conduct this type of search.

The Exclusionary Rule and Its Exceptions

Evidence obtained in an unlawful or unreasonable search are excluded from court proceedings and are considered incompetent evidence.


Exceptions to the exclusionary rule include:

  • The good-faith exception applies when the police make an honest error in conducting the search.
  • The inevitable discovery exception applies when it is reasonable to suggest that the evidence obtained would have been discovered through legal means eventually.
  • The purged taint exception applies when the suspect’s voluntary actions outweigh the illegality of the search or seizure.
  • The independent source exception applies when the evidence is obtained from a separate source that is not directly related to the illegal search or seizure.

The 5th and 6th Amendments

The 5th Amendment protects citizens against self-incrimination.


The 6th Amendment gives individuals the right to a legal attorney during legal proceedings.


These Amendments are relevant for the admissibility of incriminating statements made by a suspect.


The police are required to give a suspect his/her “Miranda rights”, which can be waived if done intelligently and voluntarily. The Miranda warnings are as follows:


  • You have the right to remain silent.
  • Anything you say can be used against you in a court of law.
  • You have a right to have an attorney with you during the interrogation.
  • If you are unable to afford an attorney, one will be provided for you without cost.


Exceptions to the Miranda requirement include:

  • The public safety exception to Miranda is when there is immediate danger present (New York v. Quarles 1984).
  • Voluntary statements made by suspects to law enforcement during an undercover operation are admissible, as long as the statements were not obtained due to duress (Illinois v. Perkins 1990; Arizona v. Fulminante 1991).
  • Voluntary statements obtained for the purpose of impeachment are an exception to Miranda (Oregon v. Haas 1975).
  • When a suspect is silent and neither invokes nor waives his/her Miranda rights, the police are free to continue questioning (Berghuis v. Thompkins 2010).
  • Roadside questioning of motorists is also an exception to Miranda warnings.
You Have the Right - Origin of Miranda Rights

References and Supplemental Resources