1. Authority to Detain and Arrest; Use of Force
Constitutional Law
12th Edition
The University of Adelaide, School of Computer Science
6 April 2019
Chapter 3
Authority to Detain and Arrest; Use of Force
Chapter 2 — Instructions: Language of the Computer 1

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Introduction
The right of the people to be secure in their persons against unreasonable seizures, shall not be violated, and no Warrants shall issue, but upon probable cause, supported by Oath or
affirmation, and particularly describing the persons to be seized.
— The Fourth Amendment
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Seizure 
A seizure occurs when a suspect:
submits to a police officers show of legal authority
the officer gains actual physical control over the suspect
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Unreasonable Seizure
A seizure may be considered unreasonable if the officer: 
lacked adequate grounds for the seizure
failed to procure a warrant in a situation in which one was required
used excessive force to effect the seizure
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Voluntary Encounters
Encounters are considered voluntary only if the police do not:
restrict the suspect’s freedom of movement
communicate that compliance with their request is mandatory through: 
words
conduct 
gestures 
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Reasonable Suspicion
Officers, in order to satisfy the reasonable suspicion standard, must be able to:
point to behavior of the detainee that is different from what one might ordinarily expect of an innocent person in the vicinity
explain why the detainee's behavior suggests the possibility of criminal activity
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Terry Stop
The purpose of a Terry stop is to enable the police to investigate the circumstances that prompted the stop in order to confirm or dispel their suspicion within a relatively short period.
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8. Constitutional Terry Stop
For a Terry stop to be lawful, officers must:
have reasonable suspicion to initiate the stop
conduct the stop as expeditiously as possible
employ the least intrusive means of detention and investigation reasonably available
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9. Prohibited during Terry Stops
taking detainees to the police station
searching detainees for anything besides a weapon
making unnecessary displays of force
moving the detainee unnecessarily to a second location
delaying completion of stop to investigate matters beyond its scope
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Checkpoints 
In order for a checkpoints to be lawful under the Fourth Amendment, they must:
further a special need beyond the normal need to control crime
be authorized by a supervisory-level department official
be operated under systematic procedures that limit discretion in selecting vehicles to stop
be conducted so as to avoid unnecessary fear, danger, and inconvenience to motorists 
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11. Arrest Warrant Advantages
ensures admissibility of evidence seized during a search incident to the arrest
protects the officer against liability in a civil suit
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12. Arrest Warrant Requirements
magistrate must make an independent determination that probable cause exists for the arrest
magistrate's determination must be supported by information given under oath
must contain a particularized description of the person to be arrested
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13. Fourth Amendment and Use of Force
seriousness of the crime
whether the suspect poses an immediate threat to the safety of the officer or others
actively resists arrest
attempts to flee
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Use of Deadly Force
Deadly force is allowed only when the officer has probable cause to believe that such force is necessary for:
self defense
protecting others from bodily harm
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