In the 1966 case Stovall v. Denno, Warden, the U.S. Supreme Court ruled on a matter of due process in relation to identification procedures used by law enforcement during criminal investigations. The petitioner, Stovall, was convicted of murder based largely on an eyewitness identification made while he was under police custody at a hospital where the victim lay critically injured. He argued that this "show-up" procedure (where only one suspect is presented for identification) violated his right to due process as it was suggestive and conducive to mistaken identity. However, the court held that although such practices could be unfair and unreliable leading to misidentification; they were not necessarily unconstitutional if justified by necessity - like in this case where immediate action was needed given victim's critical condition who later died without regaining consciousness again after identifying Stovall as her attacker.

In the dissenting opinion for Stovall v. Denno, Justice William O. Douglas argued that the majority's decision not to apply a new constitutional rule retroactively was inconsistent with previous court decisions and undermined the principle of equality under law. He contended that if a courtroom practice is found unconstitutional, it should be deemed as such regardless of when it occurred. By failing to apply this standard retroactively, he believed that individuals who were convicted under old rules would continue to suffer from an unfair trial process even after those practices had been declared unjust by the Supreme Court itself.