Probable cause refers to the reasonable belief that an individual will commit or has committed a crime or other violation. Without first establishing probable cause, any criminal search of the person’s body, belongings, or property will be deemed unreasonable. What this means is that anything that the search reveals will most likely be unusable when convicting the defendant. In order for a reasonable belief to exist, there must be factual evidence to support the suspicion. 

Generally speaking, probable cause requires more than a mere suspicion that a suspect committed a crime, but not enough information to prove that the person is guilty of a crime (beyond a reasonable doubt). The belief must be based on factual evidence, not simple suspicion. 

A common example of this would be situations in which a police officer decides to pull someone over on the highway. If the driver is swerving, speeding, braking suddenly, or driving erratically, it could be sufficient evidence to cause the police officer to have probable cause that the person is driving while under the influence. The police can then pull over the suspect based on their swerving, which provides probable cause for the stop. 

However, if the driver is driving normally and obeying all traffic rules, the police might not be able to pull the person over for drunk driving. This is due to the fact that they have no probable cause to believe that the person is driving while drunk. 

In general, the court that is issuing the warrant employs a test designed to determine whether probable cause exists. This test is based on whether an objective person of reasonable intelligence would believe that the circumstances indicate that the person arrested or detained has committed or is in the process of committing a crime. And, in situations in which police officers are allowed to make a warrantless arrest, or conduct a warrantless search or seizure, probable cause is still required. 

What Are the Sources of Probable Cause?

In order for an arrest, search, or seizure of property to be legal, an officer must prove probable cause to a judge or magistrate. There are four general categories of evidence that an officer may rely on when establishing probable cause. 

Evidence from any of these four categories would most likely allow an officer to perform a lawful arrest or perform a search:

  • Observation: Any information that is obtained by an officer through observation may be used to establish probable cause. Common examples of probable cause based on observation could include anything within the “plain view” or “plain smell” of an officer, or anything else based on what an officer sees, hears, smells, or feels. Additionally, police dogs may also conduct searches wherein the evidence discovered is admissible;
  • Circumstantial Evidence: Additionally, an officer may rely on indirect evidence that implies something has occurred, but does not directly prove it. An example of this would be how an officer responding to a robbery may have probable cause for arresting or searching a person found to be hiding in an alleyway, or running away from the scene with bags in hand. Although the evidence of the person fleeing might not directly prove that they committed the robbery, the circumstantial evidence provides probable cause for an officer to conduct a search;
  • Expertise: An officer may use their expertise and training to identify certain movements, gestures, preparations, or tools as tending to indicate criminal activity. An example of this would be how an officer may use their expertise on drug paraphernalia to establish probable cause that the items may have been used in relation to drug crimes. However, expertise and training could be considered relative, and should be utilized in conjunction with other categories of evidence; and
  • Information: An officer may use information that they have obtained from reliable sources in order to establish probable cause. Such information could include: statements by witnesses or victims, receiving information from an informant, or responding to a call made on a police scanner/radio. Recently, information obtained from an informant has been scrutinized by the Courts, especially when the information was obtained through an anonymous tip. 

It is important to note that a person may consent to the search of their person or property, in which case probable cause is automatically created. However, the area of the search is limited based upon the consent given. And, in circumstances in which a roommate or resident gives consent to search a home, an officer may not search places that the person who gave consent would not ordinarily have access to, or continue to search the premises upon the objection by the non-consenting party. 

Evidence that is directly obtained as a result of a search, seizure, or arrest that occurred without probable cause cannot be used in court against a defendant charged with the commission of a crime. As such, if a search or arrest was made with or without a warrant, and probable cause was not sufficiently established, the evidence obtained without probable cause may be suppressed in court. 

When Can a Legal Search, Seizure, or Arrest Occur?

As previously discussed, probable cause must exist before a search, seizure, or arrest by law enforcement can lawfully be conducted. Additionally, search warrants and arrest warrants are only issued upon a finding of probable cause by a judge or magistrate. Generally speaking, a judge must sign an order for a search warrant in connection with a crime; a judge will usually only authorize police to search a person or property after determining there is enough probable cause to do so. 

Warrantless searches or arrests must also meet the standard of probable cause to be admissible in court. Although such steps could cause an investigation to last longer, they are necessary to protect the privacy rights and constitutional rights of the potential suspects involved. 

However, the motor vehicle is exempt from the search warrant requirement. What this means is that police may search a motor vehicle without a warrant, but probable cause is still needed. As such, the police can search any part of the vehicle so long as they have probable cause that they will find contraband or evidence of a crime. This includes any containers inside the motor vehicle, such as glove boxes or the trunk of the vehicle.

What Makes a Search Legal?

In order to better understand the definition of probable cause, it is helpful to also discuss what makes a police search legal. According to state and federal criminal laws, an illegal search is one that is conducted by police without a search warrant, and/or with unreasonable suspicion. 

The 4th Amendment of the U.S. Constitution is what protects citizens from unreasonable searches and seizures of property. In order to lawfully search a person’s body or their property, the police must have probable cause. This is how a legal search relates to the legal definition of probable cause.

Is Probable Cause the Same as “Beyond a Reasonable Doubt”?

While the two concepts are related and often interact with each other, they are not the same. Police need probable cause in order to conduct a search. However, once a case goes to trial, the defendant must be proven guilty “beyond a reasonable doubt”. This is the level of proof required to show that the defendant is indeed guilty. This is a fairly high standard to meet, and is instituted to help protect criminal defendants. 

To simplify: “probable cause” is the level of suspicion needed before police can conduct a search or investigation, whereas “beyond a reasonable doubt” is the level of proof needed in criminal trials to find a defendant guilty.

Should I Contact a Lawyer if I’m Facing Issues Involving Probable Cause?

If you do not believe that an officer had probable cause to search you, you should immediately consult with a well qualified and knowledgeable criminal lawyer in your area. An experienced criminal attorney will be able to inform you of your legal rights and defenses to the search or arrest. Finally, an experienced and local criminal defense attorney will also be able to represent you in court as needed.