Many times when people are questioned by the police, they don't feel that they are free to walk away from the officer. However, until you've been formally detained (as in a traffic stop) or arrested, the officer can't stop you from simply walking away. Once the officer prevents you from walking away, an arrest has taken place. Whether it is a legal arrest or not depends in large part on whether the officer had "probable cause."

What is Probable Cause?

The Fourth Amendment of the U.S. Constitution authorizes police to make an arrest as long as they have "probable cause." More specifically, the Fourth Amendment states:

The right of the people to be secure in their persons, houses, papers, and effects, against unreasonable searches and seizures, shall not be violated, and no Warrants shall issue, but upon probable cause, supported by Oath or affirmation, and particularly describing the place to be searched, and the persons or things to be seized.

The idea behind probable cause is to prevent the sort of police states that exist in other countries, where officials can simply round up people they don't like as "undesirables" or "threats" without any justification. This standard is deliberately vague, but over time the interpretation of what constitutes a legal arrest based on probable cause has become fairly solidified.

Probable Cause is established through factual evidence, and not just suspicions or hunches and can be based on:

• Observation alone (sight, smell, sound, etc.), including observations that create suspicion based on a familiar pattern of criminal activity, such as when an officer sees a car circling around an area repeatedly or when someone is flashing their headlights.
• Information derived from witnesses, victims and informants.
• Police expertise, such as recognition of gang signs, detection of tools appropriate for committing certain crimes, or knowledge of movements and gestures that indicate criminal activity.
• Circumstantial evidence that only indirectly indicates that a crime has occurred, such as a broken window.

Who Decides Whether an Officer had Probable Cause?

While probable cause needs to be established before an arrest by the police officer, probable cause can be determined after the fact by a judge. This means that an officer could have a reasonable good faith belief that they had probable cause, but a judge can later determine that there was in fact no probable cause. If this occurs, evidence acquired without probable cause becomes inadmissible in court.

Also, even if it turns out that the police were wrong and a suspect is later acquitted, it doesn't affect the determination of probable cause. Probable cause is extremely important to the police, because even if the suspect is found to be innocent, the finding of probable cause shields the police from lawsuits.

How Much Evidence is Enough to Establish Probable Cause?

There is no set amount of information and no hard rule for what constitutes enough information to establish probable cause. The standard is meant to be flexible, and allows judges to balance the rights of the police to conduct investigations and protect the populace in good faith, against the rights of citizens to not be harassed by the police. Judges will often make their decision on whether probable cause existed based on their:

• Interpretations of what the drafters of the Fourth Amendment meant to protect
• Views on the police, government interference and defendant's rights
• Experience in deciding similar factual situations
• Experience with prior cases involving the arresting officer

Was Your Arrest Legal? Get Help From an Attorney Today

Not all arrests are legal arrests. Probable cause is not always clearly defined and can vary based on the facts of any case. If you're facing an arrest or have already been arrested, you may be able to challenge the basis for your arrest, and any evidence derived from it. Time can be of the essence in a criminal case, so be sure to reach out to an experienced criminal defense attorney in your area soon.