Criminal.law · Glossary
Probable cause
A plain-language definition of probable cause: what it is, where it comes up in U.S. criminal cases, and who decides it, with federal, Florida and Mississippi examples.
Editorial direction: Antonio G. Jimenez · Former prosecutor and former criminal defense attorneyPublished General legal information, not legal advice · Editorial standards
Key takeaways
- The Fourth Amendment requires probable cause, supported by oath or affirmation, before a warrant may issue. [1]
- In federal court, a magistrate judge decides at a preliminary hearing whether there is probable cause that an offense was committed and that the defendant committed it. [11]
- Under both the federal and Florida rules, a finding of no probable cause does not by itself end the possibility of later prosecution. [11][5]
What is probable cause?
Probable cause is the legal threshold that must be met before certain steps in a U.S. criminal case can happen. The U.S. Constitution says no warrant may issue without it. Federal court rules frame the question as whether there is probable cause to believe that an offense was committed and that the defendant committed it. Federal court and the states each apply the term through their own procedures. [1][8]
Where does probable cause come up in a criminal case?
Probable cause comes up at several early checkpoints: when a warrant is sought, when a person is held after arrest, and at a preliminary hearing. Criminal procedure is mostly set by each state, and federal court has its own rules. This page uses the U.S. Constitution, the federal rules, and examples from Florida, Mississippi and Nebraska. It does not describe every state. [1]
The first checkpoint is the warrant. The Fourth Amendment allows warrants only on probable cause supported by oath or affirmation. In federal court, a judge must issue an arrest warrant when the complaint or supporting sworn statements (affidavits) establish probable cause that an offense was committed and that the defendant committed it. At the government's request, the judge issues a summons instead. [8]
The second checkpoint is detention after arrest. Florida's rule requires a nonadversary probable cause determination for a defendant in custody, within a time limit the rule sets. "Nonadversary" means the defense does not contest the question at that proceeding. The determination is not required when a judge already found probable cause and issued an arrest warrant for the specific offense. [9]
The third checkpoint is the preliminary hearing, a court hearing where a judge decides whether the case can go forward. In federal court and in Florida's adversary preliminary hearing, the question is whether there is probable cause that an offense was committed and that the defendant committed it. [11][2]
Who decides whether there is probable cause?
In the rules covered here, a judge decides. In federal court, that is usually a magistrate judge. A federal magistrate judge conducts the preliminary hearing and decides whether probable cause exists. Mississippi's rule likewise directs the judge to determine probable cause at a preliminary hearing. [11][3]
In Florida's nonadversary determination, the judge decides whether there is probable cause to keep the arrested person detained. The judge applies the same standard used for issuing an arrest warrant. The defendant does not need to be present. [4]
What happens if a judge finds no probable cause?
In federal court, if the magistrate judge finds no probable cause, the judge must dismiss the complaint and discharge the defendant. The rule also says that a discharge does not prevent the government from prosecuting the same offense later. [11]
Florida's rule provides for release when probable cause is not found. That release does not end further prosecution by information (a prosecutor's charging document) or by indictment (a grand jury's charge). It does bar any restraint on liberty other than appearing for trial. [5]
Can a defendant argue at a federal preliminary hearing that evidence was gathered illegally?
Not under the federal rule. At a federal preliminary hearing, the defendant may cross-examine adverse witnesses and introduce evidence. The defendant may not object to evidence on the ground that it was unlawfully acquired. Challenges to how evidence was obtained are generally raised in other proceedings, such as a motion to suppress. [11]
Is there always a preliminary hearing on probable cause?
No. In federal court, a preliminary hearing is required for offenses other than petty offenses. The federal rule lists exceptions, including when the defendant waives the hearing or is indicted. Nebraska's court rules also describe how a defendant may waive the preliminary hearing. Other states set their own rules. [10][6]
Does probable cause apply to searches and property, not just arrests?
Yes. The Fourth Amendment's probable cause requirement covers warrants to search places and to seize persons or things. Some state laws also use the term for property. For example, a Florida statute provides for a court hearing on whether there is probable cause to believe certain material is obscene. [1][7]