Probable Cause vs. Reasonable Suspicion — Why It Matters

Defining reasonable suspicion in California

Reasonable suspicion lets officers briefly detain a driver when they can point to facts suggesting DUI or another offense. It’s less than probable cause but more than a hunch. The concept comes from Terry v. Ohio and was applied to traffic stops in People v. Wells, which approved a stop based on a reliable citizen report of erratic driving but rejected vague observations.

Probable cause — the higher standard for arrest

Probable cause requires facts that would lead a reasonable person to believe a DUI was committed—such as failed field tests, odor of alcohol, or admissions. An arrest without probable cause violates the Fourth Amendment and leads to suppression under § 1538.5.

Why this difference matters

The line between suspicion and cause defines whether evidence survives. A stop lacking reasonable suspicion invalidates later evidence; an arrest without probable cause voids the prosecution’s case. Attorneys exploit this gap to suppress unlawfully obtained evidence—often ending DUI cases outright.

Examples of police overreach in DUI stops

• Minor weaving: A single drift within a lane isn’t enough (People v. Perez (1985) 175 Cal.App.3d Supp. 8).
• Late-night profiling: Time or location alone don’t justify detention (People v. Miranda (1993) 17 Cal.App.4th 917).
• Checkpoint errors: Ignoring neutral selection or signage requirements violates Ingersoll v. Palmer.
• Pretext without violation: Even if DUI is suspected, officers must cite a specific Vehicle Code infraction (VC Division 11).

Challenging an unlawful stop or arrest

Defense attorneys file a motion to suppress under Penal Code § 1538.5. The court examines only what the officer knew when activating lights or making the arrest.

• Secure dash-cam and body-cam footage to compare to the report.
• Analyze dispatch logs and 911 audio for corroboration.
• Cross-examine discrepancies between reports and video timing.

Consequences of violating the standard

Evidence from an unlawful stop or arrest is excluded as “fruit of the poisonous tree.” The prosecution must dismiss or reduce charges. See People v. Souza (1994) 9 Cal.4th 224.

FAQs

How do reasonable suspicion and probable cause differ?

Suspicion permits brief detention; probable cause permits arrest or search. Both must rely on objective facts.

Can an officer stop me just for driving late at night?

No. Time and location alone don’t justify detention (People v. Miranda).

Are DUI checkpoints exempt from reasonable-suspicion rules?

They don’t require individualized suspicion but must follow neutral administrative protocols per Ingersoll v. Palmer.

What evidence proves a stop was unlawful?

Video footage, dispatch data, and 911 audio often contradict officer claims and show a lack of objective facts.

Talk with Braden & Tucci

Our firm has argued hundreds of suppression motions throughout Southern California, exposing unlawful stops and arrests. Call (949) 996-0170 or visit caduilaw.com for a free consultation today.

Disclaimer: This article is for informational purposes only and not legal advice. Outcomes depend on specific facts and jurisdiction.