People are often shocked to learn how little police need to arrest them. There is no requirement that officers be sure you committed a crime — or even that it be more likely than not. The legal standard is called probable cause, and understanding it explains both why arrests happen so easily and how they can be challenged afterward.
What probable cause means
Probable cause exists when the facts and circumstances known to the officer would lead a reasonable person to believe that a crime has been committed — and, for an arrest, that the person being arrested committed it. For a search, the same standard applies to believing evidence will be found in the place to be searched.
Notice what probable cause is not:
- It is not proof beyond a reasonable doubt — that is the standard for conviction at trial, and it is far higher.
- It is not a hunch, a profile, or a feeling. Officers must be able to point to actual facts.
- It is not judged by what officers learned later. It is judged by what they knew at the moment of the arrest.
What officers typically rely on
Probable cause is usually built from some combination of:
- The officer's own observations — driving patterns before a DUI stop, the smell of alcohol, slurred speech, contraband in plain view
- Statements from witnesses or alleged victims — a single person's account can be enough, even if it later turns out to be wrong
- Evidence at the scene — injuries, damaged property, items matching a reported theft
- Admissions — which is why what you say during an encounter matters so much, and why silence is protective
Arrests with and without a warrant
Under Penal Code § 836, an officer may arrest without a warrant for a felony whenever there is probable cause to believe the person committed it — whether or not it happened in the officer's presence. Misdemeanors are different: as a rule, a warrantless misdemeanor arrest requires the offense to occur in the officer's presence, with exceptions (including many DUI and domestic-violence situations).
If you are arrested without a warrant, a judge must review the probable cause for your continued detention promptly — generally within 48 hours — and your arraignment follows on a similar clock.
When there is no probable cause — and why it matters
An arrest without probable cause violates the Fourth Amendment, and it can change the entire case:
- Evidence can be suppressed. Under Penal Code § 1538.5, evidence obtained through an unlawful arrest or search can be excluded — and without that evidence, cases are routinely reduced or dismissed.
- Probable cause is tested early. At a preliminary hearing in a felony case, the prosecution must show probable cause to hold you to answer; a judge decides, not the arresting officer.
- Statements can fall with the arrest. Confessions and admissions obtained after an unlawful arrest are themselves at risk of exclusion.
This is why "the police had no right to arrest me" is not an argument to make on the street — it is an argument your lawyer makes in court, with the police reports, body-camera video, and dispatch records in hand.
Arrested is not convicted
An arrest means an officer believed there was probable cause. It says nothing about whether a prosecutor will file charges, whether the evidence will survive challenge, or whether a jury would ever convict. Some of the best outcomes in criminal defense — charges declined, cases dismissed — begin with arrests that looked bad on day one.
If you or a family member has been arrested in the San Gabriel Valley, Perliss Law Firm can review the arrest itself, not just the charge. Our team is led by a former prosecutor, our phones are answered 24/7 in English and Chinese, and the consultation is free: (626) 323-9108.
Related reading: Arrest vs. Conviction: Why the Difference Matters · Criminal Defense
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