In the case of Foster v. California, the U.S. Supreme Court ruled in 1969 that a police lineup was so suggestive and conducive to irreparable mistaken identification that it violated due process rights under the Fourteenth Amendment. The defendant, Mr. Foster, had been identified as a robber by a victim who initially failed to identify him in two lineups but later did so after being given additional opportunities and suggestions by law enforcement officers. The court found these procedures were unduly suggestive and created an unacceptable risk of misidentification which could lead to wrongful conviction - thus violating his constitutional right to fair treatment under law (due process). This ruling emphasized the importance of ensuring fairness in criminal identification processes for defendants' protection against potential miscarriages of justice.

In the dissenting opinion for Foster v. California, Justice Harlan argued that the majority's decision to overturn Foster's conviction due to an unfair lineup was misguided. He contended that while there were irregularities in the identification process, they did not necessarily lead to a substantial likelihood of misidentification. Harlan pointed out that at each stage of identification - from photo array, line-up and courtroom confrontation - Mr. Foster was positively identified by the victim who had ample opportunity during robbery to observe him closely under good lighting conditions for several minutes which made his memory reliable enough despite procedural flaws in police conduct. The justice believed this case should have been evaluated on its own merits rather than being used as a vehicle for establishing new constitutional rules about criminal procedure and suggested more deference be given to state courts' ability to judge fairness within their own systems.