What’s the effect of an invalid arrest?
Is an unlawful arrest a defense?
What happens when the police unlawfully arrest someone who happens to be guilty of a crime? Can the defendant hold up the illegal arrest as a defense to criminal charges?
Unfortunately for some arrestees, the answer to the latter question is no: An invalid arrest, standing alone, typically has no effect on ensuing criminal charges. (Frisbie v. Collins, 342 U.S. 519 (1952).) But there’s an important distinction to make here: Evidence the police acquire because of an illegal arrest may be inadmissible in court.
Example: Officer Hauk suspects Bodie of selling cocaine, but doesn’t have any legitimate evidence to support that suspicion. When Hauk encounters Bodie on the street and Bodie mouths off to him, the enraged officer decides to make an arrest on the spot. Hauk didn’t have reasonable suspicion to detain Bodie, and he certainly didn’t have probable cause for an arrest. But, as luck would have it, other officers in Hauk’s department had been independently investigating Bodie for cocaine sales, and had just accumulated enough evidence for prosecution. Bodie doesn’t have a defense to that prosecution on the grounds that Hauk’s arrest was invalid.
Example: Same facts, but this time, after the arrest, Hauk finds a baggie of cocaine in Bodie’s pocket. Police officers are typically allowed to search suspects after arresting them (see Searches After Arrest), but because the arrest was unlawful, the search was, too. The result is that the government can still prosecute Bodie, but that (assuming the defense files a motion to suppress) it can’t use in its case evidence of the cocaine baggie that Hauk found.
BAD STOP DOESN'T ALWAYS MEAN BAD EVIDENCE
The exclusionary rule generally requires that evidence that results from an unlawful detention or arrest be excluded from court. But not always.
Suppose a warrant is out for your arrest. An officer who’s unaware of the warrant detains you, but not because you were doing anything wrong. Maybe the officer is speculating that you’re up to no good. Whatever the reason, it’s not reason enough: The policeperson doesn’t have reasonable suspicion that you have committed or are committing a crime.
The officer asks for your identification, has dispatch run a check, and learns about the warrant. The cop arrests and searches you, finding some kind of contraband in your pockets.
Even though the stop was illegal because it wasn’t based on reasonable suspicion, the contraband could very well be admissible against you in court. The U.S. Supreme Court has held, essentially, that arrest warrants can retroactively justify illegal detentions. (For much more on the rules in this area, see this article on the “attenuation doctrine.”)