Knights was on probation for a drug offense when the facts of this case occurred. One of the conditions of his probation was that he would "[s]ubmit his . . . person, property, place of residence, vehicle, personal effects, to search at anytime, with or without a search warrant, warrant of arrest or reasonable cause by any probation officer or law enforcement officer." He was notified of this condition in writing, on a form that he signed.
Whilst on probation, Knights was a suspect in an arson investigation (he was mad at the power company, which had caught him stealing electricity. There was a series of 30 vandalisms to their facilities which coincided with his court dates, and the latest involved a fire that cause $1.5 million in damage). A detective noticed the correlation, and set up surveillance at Knights' house. He saw Knights' co-conspirator disposing of pipe bombs, and saw other explosives in the back of Knights' truck. When Knights was gone, he searched the apartment and found more explosives, and a padlock with the power company's name stamped on it. Because the detective was aware of the search provision in Knights' probation, he didn't bother getting a warrant.
The evidence was initially suppressed because the search was done for investigative rather than probationary purposes. The Supreme Court held that being a probationer subject to a search provision significantly diminished Knights' privacy interests. The ruling states that "when an officer has reasonable suspicion that a probationer subject to a search condition is engaged in criminal activity, there is enough likelihood that criminal conduct is occurring that an intrusion on the probationer's significantly diminished privacy interests is reasonable." (emphasis added)
Since there was clearly RS in this case, the search was valid and the evidence admitted. The court declined to base its decision on the detective's motivation for the search, since an officer's subjective intent is irrelevant to fourth amendment analysis.