In Duckworth, Warden v. Serrano (1981), the United States Supreme Court addressed whether a prisoner's constitutional rights were violated when his mail was opened outside of his presence. The petitioner, an inmate at Indiana State Prison, claimed that prison officials had infringed on his First Amendment rights by opening and reading legal mail sent to him from courts and attorneys without him being present. He argued this practice could potentially allow for censorship or interference with confidential attorney-client communications. The court ruled in favor of the warden, stating that while prisoners do have certain protected First Amendment rights regarding their correspondence with courts and lawyers, these must be balanced against legitimate penological interests such as maintaining security within prisons. The court found no evidence suggesting that prison officials were using this policy to interfere with inmates' legal proceedings or censor their mail content; rather it was used solely for detecting contraband materials which is a valid concern in correctional facilities.

In the dissenting opinion for Duckworth v. Serrano, Justice Brennan, joined by Justices Marshall and Blackmun, argued that the majority's decision to uphold a conviction despite an incomplete Miranda warning was flawed. They contended that the warnings given did not fully inform Serrano of his rights as required by Miranda v. Arizona because they suggested he could only consult with an attorney after interrogation had begun which is misleading and incorrect. The dissenting justices believed this misrepresentation violated Serrano’s Fifth Amendment right against self-incrimination and thus his confession should have been excluded from evidence at trial. They also criticized the majority's reliance on later clarifying language in a waiver form signed by Serrano as it does not rectify or cure initial misinformation about constitutional rights.