If you've ever been arrested, it's important to be able to gauge whether the police treated you in accordance with the law. The terms "reasonable suspicion" and "probable cause" are key concepts to understand.
What is reasonable suspicion?
If a police officer has reasonable suspicion, they have an informed hunch that you have been, are or will be involved in an illegal activity. This presumption is usually based on indicators and circumstances. For instance, if you answer questions inconsistently and act nervously, this could be grounds for reasonable suspicion. Additionally, if you behave suspiciously-e.g., you're walking down the street, spot the police and immediately run in the other direction-the police could view this as reasonable suspicion.
If the police have a legitimate cause for reasonable suspicion, they have the authority to briefly stop you to conduct an investigation. If they believe you pose a threat of violence, they may also frisk you (over your clothing) to check for weapons. Refusing to answer questions or refusing search requests does not create reasonable suspicion.
What is probable cause?
Probable cause is a higher legal standard of proof. With reasonable suspicion, it appears as though there is criminal activity. With probable cause, there is hard evidence supporting this suspicion. A police officer must have probable cause in order to arrest someone, perform a search on a person or their property and obtain a warrant.
It is not enough just for a police officer to believe they had probable cause in making an arrest; a judge must also agree with their logic. If a judge determines that there was no probable cause, then any evidence obtained through search and seizure is no longer admissible in court.