The police do not necessarily require a warrant in order to arrest a person suspected of committing a crime. The Supreme Court came to the conclusion that enforcing the law would be too difficult if the police were required to obtain a warrant prior to every arrest. The delay in drafting the warrant and then finding a judge to sign it could lead to the suspect fleeing, destroying vital evidence or committing a serious crime.

In order to strike a balance between the need for law and order, and the rights of the individual, the police are allowed to arrest suspects without a warrant where it is reasonable under the circumstances, pursuant to the Fourth Amendment. For a suspect to remain in custody, thereafter, the police must quickly convince a judge that there was probable cause for the arrest.

There are at least five instances in which a warrantless arrest by a police officer will be deemed reasonable:

A felony has been committed in a public place.

An officer who reasonably believes that a felony is taking place is entitled to stop the suspect and conduct a search of the suspect’s outer clothing for weapons or anything that might harm the officer. If the officer asks for identification and the suspect refuses to show it, this may give rise to probable cause for an arrest.

A felony committed in a place not open to the public usually requires a warrant, unless the police are chasing a fleeing suspect, such as someone who they have good reason to believe has just robbed a jewelry store.

A misdemeanor occurs in the presence of a police officer.

Where a misdemeanour is not committed in the presence of a police officer, warrantless arrests are generally not acceptable, unless otherwise provided by statute or state constitution. All five senses may be used to determine whether the offense was committed in the officer’s presence. The judge will consider what the officer saw, smelled, felt, heard or tasted.

A traffic law infraction is believed to have taken place.

For example, a vehicle may be stopped when the police officer believes that the driver was speeding. The penalty for this type of offense is usually a traffic ticket resulting in a fine or forfeiture, rather than a warrantless arrest, although such an arrest is possible. The officer is allowed, by law, to search the inside of the stopped vehicle including the glove compartment, but not the trunk unless he/she has reasonable suspicion to believe that it contains evidence of criminal activity. If an officer sees white powder on a seat, for example, and a search of the interior reveals an illegal parcel of cocaine, the officer may make an arrest on the spot.

The police are unaware that they have a defective warrant.

Technically, they have no authority to affect an arrest. A warrant may be considered defective when it fails to meet the requirements for a properly executed warrant. The warrant must conform to the form required by law. That is, it must:

  • Contain the defendant’s name, or a name by which he/she can be identified with reasonable certainty
  • Describe the offense charged in the complaint
  • Command that the defendant be arrested and brought without unnecessary delay before a magistrate judge
  • Be signed by a judge

However, if the police officers were acting in good faith and did not abuse their authority when arresting the suspect, the arrest may still be considered reasonable, provided that the defect was not due to police attempts to deceive the magistrate who signed the warrant. To declare the arrest unlawful in such circumstances would punish honest police officers and allow the suspect to be released.

Exigent circumstances justify an arrest in a home.

In order to arrest a suspect in their home, the police would generally require an arrest warrant. In such situations, the police would place officers in a position to watch the premises to prevent the suspect’s escape while the warrant is being sought.

However, there are circumstances where a warrantless arrest in the suspect’s home will be acceptable. Any warrantless arrest by police must be justified by exigent circumstances. In order to assess whether exigent circumstances vindicated the police’s conduct, a court will look at all the circumstances surrounding the arrest including the seriousness of the offense, the chance of the suspect destroying evidence, danger to any individual in the home, and the possibility of the suspect escaping. Those surrounding circumstances must amount to an emergency in order to justify an arrest. If a victim is screaming inside and the police gain entry and hold the suspected attacker, then this would likely be considered sufficiently exigent for a judge.

Remember that citizens can also make warrantless arrests under certain circumstances, which brings us to the sixth instance:

A civilian has probable cause to apprehend a suspect.

A member of the public may make a citizen's arrest if that person has probable cause to believe that an offense is taking place or has taken place. The person is permitted to use a reasonable degree of force in apprehending the suspect. Problems may arise for the citizen if the matter of the degree of force used is considered excessive, or if the citizen made a mistake and challenged an innocent person going about their lawful business. Such a citizen may be civilly liable for damages as a result of injuries to the suspect or the suspect’s reputation.