When an Oregon resident is arrested, the arrest must comply with state, federal and common law for it to be a legal arrest. Many people do not know when they are free to end a police interrogation and walk away or when they must comply.

The Fourth Amendment of the United States Constitution authorizes law enforcement to make an arrest when they have “probable cause” to believe a crime has been committed. This constitutional protection is designed to prevent governments and police from detaining and imprisoning people because they are undesirable but innocent of any crime.

Probable cause must be established through factual evidence. This includes observation by law enforcement, police expertise, witness statements and circumstantial evidence that indirectly suggests a crime has occurred.

A determination of probable cause is subject to judicial review. A finding of probable cause is extremely important to law enforcement because if police had a reasonable belief that there was probable cause at the time an arrest occurred, they will be shielded from liability even if a person is later proven innocent.

There is no set amount of information required to establish probable cause. The standard was designed to be flexible in order to balance the rights of citizens with the needs of law enforcement. Judges will usually base their decisions on their knowledge of relevant case law and experience with similar situations.

A criminal defense attorney may be able to help defendants who want to challenge a recent arrest. Not every arrest is legal. A criminal defense attorney may be able to help clients who believe they were illegally arrested by investigating the case, reviewing evidence, interviewing witnesses, filing pre-trial motions, researching similar cases and making oral arguments at a pre-trial hearing.

If a judge rules that an arrest was illegal, it might result in exclusion of certain evidence or dismissal of the case. In some cases, it may be possible to sue law enforcement personnel who made the illegal arrest.