In the case of Castille, District Attorney of Philadelphia County, et al. v. Peoples in 1988, the U.S Supreme Court ruled that a prosecutor's office could not be held liable for providing incorrect information to police during an investigation which led to wrongful arrest and prosecution. The plaintiff, Peoples had been arrested based on false information provided by a secretary in the district attorney’s office who misidentified him as a suspect in an armed robbery case. He was detained for several days before being released without charges filed against him due to lack of evidence linking him with the crime scene. Peoples sued both individual prosecutors and their offices under Section 1983 alleging violation of his constitutional rights but lost at trial court level and appealed up to Supreme Court arguing that he should have been able to sue because they were acting outside their role as advocates when giving advice during investigations. However, Justice Antonin Scalia writing for majority upheld lower courts' decisions stating that prosecutorial immunity extends even when prosecutors are offering legal advice during criminal investigations since it is intimately associated with judicial phase of criminal process thus protected from liability.

In the dissenting opinion for Castille v. Peoples, Justice Scalia argued that the majority's decision to grant habeas corpus relief was incorrect because it failed to respect Pennsylvania Supreme Court's interpretation of its own laws. He contended that federal courts should not interfere with state court decisions unless there is a clear violation of constitutional rights, which he did not believe occurred in this case. Furthermore, he disagreed with the majority’s view on “harmless error” analysis and believed that any potential bias from one judge out of five would have been inconsequential to the final verdict. In his view, even if District Attorney Ronald Castille had previously participated as prosecutor in defendant Terrance William’s murder trial before becoming a justice who denied Williams' post-conviction appeal, it wouldn't necessarily lead to an unfair judgment given other justices’ involvement in deciding cases collectively.