In Roviaro v. United States, the U.S. Supreme Court ruled that the government's interest in protecting the identity of an informant must be balanced against a defendant's right to prepare his defense. The case involved John Roviaro who was charged with selling heroin based on information from an undisclosed informant. The court held that under certain circumstances, such as when the informer is a key witness or participant in the crime, their identity should be disclosed if it would significantly aid a defendant’s case or is essential for a fair determination of cause. In this instance, since there were no other witnesses to testify about how and where he allegedly sold drugs except for this undisclosed informant, withholding their identity violated Roviaro’s rights under due process clause of 14th Amendment and reversed his conviction.

In the dissenting opinion for Roviaro v. United States, Justice Tom C. Clark disagreed with the majority's decision to reverse and remand the case back to lower courts due to non-disclosure of an informant’s identity by law enforcement officers. He argued that this ruling could potentially jeopardize future undercover operations and investigations as it would require revealing informants' identities in court proceedings, thereby endangering their lives or making them reluctant to cooperate with law enforcement in the future. Furthermore, he contended that there was no constitutional requirement mandating such disclosure and believed that whether or not an informant's identity should be revealed should depend on a case-by-case basis rather than being established as a blanket rule.