Probable Cause

What It Is

Probable cause exists when the facts and circumstances known to the officer would lead a reasonable person to believe that a crime has been, is being, or is about to be committed (for arrest), or that evidence of a crime will be found in a particular place (for search).

It’s more than a hunch. More than reasonable suspicion. But less than proof beyond a reasonable doubt. Think of it as a “fair probability.”

Why It Matters

An arrest without probable cause violates the Fourth Amendment. That’s the basis of an unlawful arrest claim under § 1983.

The officer doesn’t need to be right. They need to have had a reasonable basis for believing you committed a crime at the time of the arrest. Evidence discovered later doesn’t retroactively create probable cause, and the fact that charges were dropped doesn’t prove there was no probable cause.

The Practical Problem

Probable cause is a low bar. Officers can point to almost anything — furtive movements, “matching a description,” “odor of marijuana,” nervous behavior — and courts will often find probable cause existed.

For pro se plaintiffs challenging an arrest, you need to show that the stated basis for the arrest was objectively unreasonable. If the officer fabricated the basis, even better — but you need evidence.

Key Cases

• Illinois v. Gates, 462 U.S. 213 (1983) — “Totality of the circumstances” test for probable cause
• Maryland v. Pringle, 540 U.S. 366 (2003) — Probable cause is a “practical, nontechnical” standard
• Devenpeck v. Alford, 543 U.S. 146 (2004) — Probable cause assessed objectively; officer’s stated reason doesn’t matter if objective probable cause existed for any offense