What Is Probable Cause?

Probable cause is a legal requirement found in the Fourth Amendment of the United States Constitution. 

In general, probable cause exists when the police have a reasonable basis for believing that a crime has been committed or that evidence is likely in a particular location. Specific facts and circumstances must logically support probable cause. When the police act without probable cause, it is a constitutional violation.

What Do Police Need Probable Cause For?

The police need probable cause to arrest someone, conduct a search, or get a warrant. If the police don’t have probable cause, they are acting illegally.


To arrest someone, the police need probable cause that a crime has been committed by this particular individual. This applies whether or not the arrest is pursuant to an arrest warrant. The police must consider the totality of the circumstances, meaning all information they know at the time of the arrest. 


To search, with or without a warrant, the police must have a fair probability that evidence of a crime will be discovered in a particular location. This is based on their reasonable opinion and expertise. This rule applies to all searches, including homes, people, and cars.


A warrant is a legal document, authorized by a judge, that gives police the authority to search or arrest someone. The law favors warrants, but they are not required as long as there is probable cause.

To get a warrant, a police officer must go before a judge and explain the probable cause. They provide either a written or oral affidavit. If the judge decides that there is sufficient probable cause, they issue the warrant.

How Much Evidence Equals Probable Cause?

Probable cause is tricky because no set amount of evidence is required. The police do not need nearly the same amount of evidence to convict someone of a crime. The police can rely on evidence that is not admissible in court, like hearsay. 

Examples of evidence include:

  • Statements from reliable witnesses
  • Photographs and surveillance footage 
  • Police observations 
  • Physical evidence, like DNA or fingerprints
  • Records 

The police do not need to list all of the evidence to get a warrant. They only need to meet the probable cause threshold. 

Probable Cause Vs. Reasonable Suspicion

Probable cause is a higher standard than reasonable suspicion. Probable cause requires some evidence, even if circumstantial. 

Reasonable suspicion is a lower standard, closer to a hunch or reasonable inference. Reasonable suspicion is required for the police to stop someone temporarily or conduct a limited patdown for weapons (also known as a frisk). Reasonable suspicion must be based on specific and articulable facts. 

In Terry v. Ohio, the police observed three men continuously walking back and forth past the same business. They were peering into the window and then would stop and talk on the corner. The policeman was suspicious that the men were planning to rob the business and were “casing the joint.” As a result, he approached the men, frisked them for weapons, and found guns. This created probable cause for an arrest.

The Court said that the policeman had reasonable suspicion to conduct the stop and frisk and probable cause for the arrest after the patdown.

Common Exceptions to the Probable Cause Requirement

There are several well-established exceptions to the probable cause requirement. 

Search Incident To Arrest

If the police lawfully arrest someone, they can search that person and areas in their immediate control. This is for safety (to ensure that the person doesn’t have any weapons) and to preserve evidence of the crime.

Plain View

Sometimes the police get a search warrant for a particular location in a house, like a bedroom. If the police observe evidence or something illegal in plain view on the way to the bedroom, they can seize it. Plain view means that the police do not need to move, uncover, or open anything to observe the item.

This often comes into play during traffic stops. If the police officer stops a driver and sees drugs sitting on the passenger seat in plain view, the police can seize them, even if they didn’t have probable cause to search the car. 

The police often ask people to consent to searches of their car or their house. Many people consent because they mistakenly believe that the police will be more lenient with them. Unfortunately, this isn’t the case.

If you consent to a search, then the police do not need probable cause. Many police officers routinely ask drivers to search their cars, even if they don’t have probable cause. If you consent and they find something illegal, you have waived your right to argue that there was no probable cause.

Exigent Circumstances/Hot Pursuit

Exigent circumstances are something that requires immediate action. The police can bypass the warrant and probable cause requirement in an emergency. For example, if they believe that someone is about to be harmed, they can enter a home without a warrant to prevent it. 

Hot pursuit is similar to exigent circumstances. If the police are pursuing a suspect and they enter private property, the police can enter the property without a warrant. This makes sense because stopping to get a warrant would give time for the suspect to get away.

What Happens If There Is No Probable Cause?

If there is no probable cause, then the judge will not issue a warrant. 

If you are arrested or indicted without a warrant, your lawyer can argue that there was not sufficient probable cause to arrest or charge you. As a result, the case will be dismissed.

If the police search your house or car without probable cause, your lawyer can file a motion to suppress. If you win the motion to suppress, the prosecutor cannot use the evidence against you. Depending on the evidence, this may result in a dismissal.

Were you recently arrested for a crime and have questions about law enforcement’s probable cause to do so? Reach out to a trusted San Diego criminal defense lawyer for legal help.