What Is Probable Cause?

Probable cause must be based on factual evidence and not just on suspicion.

Most probable cause sources can be placed into four categories. These categories are:
  • Observation – This is information that the officer obtains through their senses, such as sight, smell or hearing. This category is also used when an officer detects a familiar pattern of criminal activity that contains suspicious behaviors (i.e., flashing headlights, circling around a certain neighborhood.)
  • Expertise – These are skills that officers are specially trained in, such as: being able to read gang graffiti and tattoos, detecting tools that are used in burglaries or knowing when certain movements or gestures indicate that a criminal activity is about to occur.
  • Information – Statements provided by witnesses and victims, information provided by informants, and announcements made through police bulletins and broadcasts.
While there are some sources of probable cause that need to be supplemented by other sources, some sources are sufficient enough to stand on their own.

For a judge to issue a search warrant, probable cause must show that it is likely that a crime took place and the person who is accused was involved in the criminal activity. If a search or arrest is made without a warrant, it must meet the standard of probable cause to be admissible in court.

Evidence obtained through searches and seizures made without probable cause can not be used against a defendant in court.