## Facts

- Mark James Knights was convicted in California of a drug offense and placed on summary probation.
- As a probation condition, Knights agreed in writing to submit his person, residence, vehicle, and effects to warrantless searches “at anytime,” with or without a warrant or reasonable cause, by probation or law enforcement officers.
- A sheriff’s detective suspected Knights of involvement in crimes using incendiary materials and, knowing of the search condition, developed reasonable suspicion of Knights’s criminal activity.
- The detective conducted a warrantless search of Knights’s apartment and vehicle and found evidence later used to indict Knights in federal court for arson-related conspiracy, possession of an unregistered destructive device, and felon-in-possession of ammunition.
- Knights moved to suppress the evidence as the product of an unreasonable search under the Fourth Amendment.

## Issues

1. Whether the Fourth Amendment limits warrantless searches conducted under a probation search condition to those serving a supervisory (“probationary”) purpose rather than ordinary law enforcement investigation.
2. Whether a warrantless search of a probationer’s home conducted under an express search condition is reasonable when supported by reasonable suspicion.

## Decision

- The Supreme Court reversed the Ninth Circuit in a unanimous opinion by Chief Justice Rehnquist.
- The Court held the warrantless search was reasonable under the Fourth Amendment because it was authorized by Knights’s probation search condition and supported by reasonable suspicion.
- The Court rejected a rule that such searches are valid only when undertaken for “probationary” purposes; investigatory purpose does not make an otherwise reasonable search unconstitutional.
- Justice Souter concurred, emphasizing the decision did not decide the constitutionality of suspicionless searches of probationers.

## Legal Principles

- Fourth Amendment validity turns on objective reasonableness assessed under the totality of the circumstances, balancing privacy intrusion against legitimate governmental interests.
- A probationer’s expectation of privacy is substantially reduced by probation status and by an express search condition accepted as part of probation.
- Where a probation search condition exists, reasonable suspicion can be sufficient to justify a warrantless search of a probationer’s residence; a warrant and probable cause are not required in that setting.
- The Constitution does not impose a “probationary purpose” limitation on searches conducted pursuant to a probation search condition; officer motive is generally irrelevant if the search is objectively reasonable.
- The Court did not determine whether agreeing to a probation search condition constitutes complete consent waiving all Fourth Amendment protections.

## Conclusion

The Court held that a warrantless search of a probationer’s residence conducted under an express probation search condition is consistent with the Fourth Amendment when supported by reasonable suspicion, and it declined to require that such searches be limited to supervisory purposes rather than ordinary law enforcement investigation.


United States v. Knights, 534 U.S. 112 (2001)