Probable cause is the presence of sufficient evidence to convince reasonable individuals that a crime has been committed, or that signs of criminal activity exist in a specific location for which the police are attempting to obtain a search warrant.
In California, the term probable cause is used in four primary situations. These are questions as to whether:
- the police have probable cause to detain you (often for a traffic stop),
- the police have probable cause to place you under arrest for a crime,
- law enforcement has presented sufficient probable cause for a search warrant to be granted, and
- the prosecutor has presented sufficient probable cause for a defendant to be held to answer at a preliminary hearing.
1. When can police stop you for a traffic violation or detain you?
Many people believe that the police can only make a traffic stop if they have probable cause. But the standard is actually “reasonable suspicion,” which is a different standard than the “probable cause” threshold.
Under California law, peace officers can only make a traffic stop if they have a reasonable suspicion that you committed a traffic violation.1
In general, reasonable suspicion is a lower standard to meet.
“Reasonable suspicion” essentially means that a reasonable person would believe that you violated a section of California’s vehicle code.2
Note that the reasonable suspicion standard also applies to stops in DUI cases. An officer can only pull you over for a possible DUI arrest if he/she has a reasonable suspicion that you are committing a crime.3
As to detentions, police officers can only stop and detain you under California criminal law if they have a reasonable suspicion that you were involved in criminal activity.4
Similar to traffic stops, a reasonable suspicion exists if a reasonable person could deduce from the facts present that you were involved in some criminal act.5
2. What standard applies to an arrest?
The police in California usually need probable cause to arrest a person without a warrant. In particular, an officer needs sufficient evidence that you:
- committed a crime in the officer’s presence, or
- committed a felony (whether or not in the officer’s presence).6
Probable cause is a slightly higher standard to meet than reasonable suspicion. It involves an arresting officer having reasonable grounds to believe that someone committed a crime. It requires more than mere suspicion, but less evidence than that required for a conviction.7
Note that in cases of an arrest warrant, a judge will issue a warrant for your arrest if they find there to be probable cause that you committed a crime.8
3. What about search warrants?
Before a California judge can issue a search warrant, they must have probable cause that:
- a crime was committed, and
- the place the police will search has evidence of a crime.9
A judge typically makes a probable cause determination by looking at the facts presented in an officer’s warrant application (also known as an “affidavit”).
“Probable cause” for searches means a reasonable belief that both a crime occurred and the search area holds evidence of the crime (for example, contraband).
4. What standard does a judge use in preliminary hearings?
Soon after a California district attorney files a felony charge, the law usually requires a court to hold a preliminary hearing.
The judge holds the hearing to determine if there is enough evidence “hold the defendant to answer” for the charges, and bind the case over for trial.
The standard used in these hearings is a probable cause standard. In other words, a judge will allow a felony case to continue if the evidence shows a reasonable belief that you committed the felony charged.
Note that probable cause is a lesser standard than the “beyond a reasonable doubt” standard used in criminal trials.
Additional reading
For more in-depth information, refer to these scholarly articles:
- Probable Cause, Probability, and Hindsight – Journal of Empirical Legal Studies
- Putting Probability Back into Probable Cause – Texas Law Review
- Probabilities in Probable Cause and Beyond: Statistical Versus Concrete Harms – Law and Contemporary Problems
- Probable Cause Pluralism – Yale Law Journal
- Probable Cause Revisited – Stanford Law Review
Legal References:
- This requirement is in the Fourth Amendment to the U.S. Constitution, which protects us from unreasonable searches and seizures on the part of law enforcement. A random traffic stop is an unreasonable seizure under the Constitution.
- Black’s Law Dictionary, Sixth Edition – “Reasonable suspicion.”
- DUI is a criminal offense under California law. The crime is most often a misdemeanor.
- See the Supreme Court case of Terry v. Ohio (1968) 392 U.S. 1. See also People v. Souza (1994) 9 Cal.4th 224 and People v. Chalak (2020) 48 Cal.App.5th Supp. 14.
- Black’s Law Dictionary, Sixth Edition – “Reasonable suspicion.”
- California Penal Code section 836 PC.
- Black’s Law Dictionary, Sixth Edition.
- California Penal Code 817 PC.
- California Penal Code 1525 PC.