Probable cause, on the other hand, is a stronger belief based on more concrete evidence. It is required for arrests or obtaining search warrants. For example, think of a traffic stop. Law enforcement officers must reasonably suspect a traffic violation or criminal activity to comply with the Fourth Amendment.
To claim a violation of Fourth Amendment rights as the basis for suppressing relevant evidence, courts have long required that the claimant must prove that they were the victim of an invasion of privacy to have a valid standing.
Some courts and scholars have suggested probable cause could, in some circumstances, allow for a fact to be established as true to a standard of less than 51%, but as of August 2019, the United States Supreme Court has never ruled that the quantification of probable cause is anything less than 51%.
Wesby, the United States Supreme Court observed that probable cause requires only a probability or substantial chance of criminal activity, not an actual showing of any criminal behaviors.
There are four categories into which evidence may fall in establishing probable cause. These include observational, circumstantial, expertise, and information: Observational evidence is based on what the officer sees, smells, or hears.
Writing a probable cause affidavit requires clarity and meticulousness. It should include date, time, location of incidents, involved officers, detailed description of the event, references to evidence, and witness statements.
Examples of probable cause include finding illegal substances during a search, witnessing a person commit a crime, or receiving credible information from an informant. However, intuition or hunches alone are not sufficient to establish probable cause under the Fourth Amendment.
Law enforcement can establish probable cause through live, sworn testimony or by a detailed affidavit describing why a warrant is necessary.
A probable cause hearing is a formal adversarial proceeding before a district court judge, but the rules of evidence are less strict and the burden of proof is lower – requiring only a “fair probability” that a crime was committed and the defendant committed it.