## Facts

- An Iowa police officer stopped Patrick Knowles for speeding and chose to issue a citation rather than make a custodial arrest, though state law allowed arrest.
- After issuing the citation, the officer conducted a full search of Knowles’s car without consent and without independent probable cause.
- The officer found marijuana and drug paraphernalia under the driver’s seat, then arrested Knowles and charged him with drug offenses.
- Iowa courts interpreted state law to permit a “search incident to citation,” allowing a full search when an officer had probable cause to arrest for a traffic offense but issued a citation instead.

## Issues

1. Whether the Fourth Amendment permits a full search of a vehicle as a “search incident to arrest” when an officer issues a traffic citation instead of making a custodial arrest.
2. Whether probable cause to make a custodial arrest, without an actual custodial arrest, is sufficient to trigger the search-incident-to-arrest exception.

## Decision

- The Supreme Court unanimously reversed and remanded.
- A full search conducted after issuance of a traffic citation, without a custodial arrest and without another independent justification, violates the Fourth Amendment.
- The traditional rationales for search incident to arrest—officer safety and preservation of evidence—did not justify Iowa’s categorical “search incident to citation” rule in this setting.
- State law authorization cannot expand the federal constitutional exception to the warrant requirement.

## Legal Principles

- The search-incident-to-arrest exception requires an actual custodial arrest; the mere existence of probable cause to arrest does not by itself justify a full search.
- Officer-safety concerns during a traffic stop may support limited protective measures, but do not automatically justify a full evidentiary search following issuance of a citation.
- Evidence-preservation rationales generally do not support a full search incident to a routine traffic citation because the evidence needed to prosecute the traffic offense is typically already obtained.
- A state cannot render a search reasonable under the Fourth Amendment by statute or judicial rule that exceeds federal constitutional limits.

## Conclusion

The Court held that issuing a traffic citation does not authorize a full search of the vehicle under the search-incident-to-arrest doctrine; absent a custodial arrest or another independent basis for a search, such a search is unreasonable under the Fourth Amendment.


Knowles v. Iowa, 525 U.S. 113 (1998)