In many places in the world, police can stop you on the street and detain you or enter your home and seize any property they think might incriminate you in a crime. To do this, they only need to have a "gut feeling" that you might be engaged in an illegal activity.
This is not the case in the United States. The Fourth Amendment of the U.S. Constitution guarantees that citizens can't be subject to searches unless government officials have "probable cause" to get a warrant from the court that allows them to arrest a citizen or search or seize property. The warrant must state specifically who is to be arrested and why, or what is to be searched.
Police have to have an adequate reason to make an arrest or search a property, just as prosecutors have to have an adequate reason to charge you with a crime.
There are times when the officer doesn't need a warrant to make an arrest, such as when a police officer sees a crime committed in public and a reasonable person would understand that a crime has either happened or is under way.
When there is a reasonable suspicion that a crime is under way or has occurred, an officer can temporarily detain a suspect. An example would be a traffic stop when an officer suspects a driver is driving under the influence of alcohol or drugs.
Authorities today wrestle with probable cause when dealing with potential mass shootings. In late November, police in Huntsville gathered to educate more than 200 people on the issue, and they discussed needing probable cause before taking action on someone they suspect might be a shooter before the actual event.
What a reasonable person would believe
Probable cause comes when the officer can show that a reasonable person would believe a crime has occurred at a specific location or that evidence of a crime exists at a specific location.
Police need a search warrant to search a property unless:
- They have consent to search a property
- The search is connected to an arrest
- There is an emergency situation that threatens public safety
- Contraband is in plain sight.
Police also cannot seize property found during a search unless a reasonable person would believe the property is contraband, stolen or is evidence of a crime.
Probable cause has to come from facts and direct observations, not from suspicion or a "gut feeling."