The Fourth Amendment governs a §1983 claim for unlawful pretrial detention even beyond the start of legal process. According to the petitioner’s complaint, he was arrested without probable cause and based solely on his possession of pills that had field-tested negative for an illegal substance. The complaint alleged that upon being brought to the police station an evidence technician tested the pills again and also got a negative result. But the petitioner alleged the technician lied in his report, claiming that one of the pills tested positive for ecstasy, a controlled substance. Also, one of the arresting officers wrote in his report that based on his training and experience, he knew the pills to be ecstasy. Another officer swore out a complaint charging the defendant with possession of a controlled substance and the defendant was brought before a judge for determination of probable cause. The judge relied exclusively on the complaint, which in turn relied exclusively on police fabrications, to support a finding of probable cause. Based on that determination, he sent the defendant to jail to await trial. The defendant’s subsequent detention was thus pursuant to “legal process” because it followed from, and was authorized by, the judge’s probable cause determination. The complaint alleged that while the defendant sat in jail, the State police lab re-examined the pills and issued a report concluding that they contained no controlled substances. For unknown reasons, however, the defendant remained in detention for another month until the prosecutor’s office sought and obtained dismissal of the drug charge. The defendant spent a total of 48 days in pretrial detention. He brought his 1983 action, alleging a violation of his Fourth Amendment rights, in part because of his detention for almost 7 weeks based on entirely made-up evidence. The lower courts dismissed his Fourth Amendment claim, finding that once a person is detained pursuant to legal process, a Fourth Amendment claim cannot be asserted. The Supreme Court rejected that analysis concluding:

[P]retrial detention can violate the Fourth Amendment not only when it precedes, but also when it follows, the start of legal process in a criminal case. The Fourth Amendment prohibits government officials from detaining a person in the absence of probable cause. That can happen when the police hold someone without any reason before the formal onset of a criminal proceeding. But it also can occur when legal process itself goes wrong—when, for example, a judge’s probable-cause determination is predicated solely on a police officer’s false statements. Then, too, a person is confined without constitutionally adequate justification. Legal process has gone forward, but it has done nothing to satisfy the Fourth Amendment’s probable-cause requirement. And for that reason, it cannot extinguish the detainee’s Fourth Amendment claim …. If the complaint is that a form of legal process resulted in pretrial detention unsupported by probable cause, then the right allegedly infringed lies in the Fourth Amendment. (Citations omitted).

The Court remanded for further proceedings.