Mark James Knights (defendant) was sentenced to summary probation for a drug conviction. As a condition of probation, Knights was ordered to allow any probation or law enforcement officer to search his person or property without a warrant or reasonable cause. Knights signed the order stating that he understood and agreed to the terms of probation. Later, a detective with the Napa County Sheriff’s Department began to suspect Knights and Steven Simoneau of committing a series of acts of vandalism against Pacific Gas & Electric (PG&E). After seeing suspicious materials in Simoneau’s truck parked in Knights’ driveway, the detective decided to search Knights’ apartment. Because of the search provision in Knights’ probation order, the detective did not believe he needed a warrant. The detective found bomb making materials and evidence of the PG&E vandalism and arrested Knights. Knights was indicted by a grand jury in federal court. Knights then moved to suppress the evidence found during the search, and the district court granted the motion because the search was conducted for investigative instead of probationary purposes. The United States Court of Appeals for the Ninth Circuit Affirmed. The United States Supreme Court granted certiorari.