In the case of Nelson, Warden v. O'Neil in 1970, the United States Supreme Court ruled on a matter concerning self-incrimination and right to counsel. The respondent, O'Neil was convicted for robbery based largely on his own pretrial statements made without having been advised of his rights or given access to legal counsel. He appealed this conviction arguing that it violated his Fifth and Sixth Amendment rights against self-incrimination and to have legal representation respectively. However, the Supreme Court held that since there was overwhelming evidence apart from these statements pointing towards O’Neil’s guilt (including eyewitness testimony), their admission did not contribute significantly to the conviction thus rendering any error harmless beyond reasonable doubt. Therefore, even though he had not been properly informed about his constitutional rights at time of making those statements as required by Miranda v Arizona ruling; this failure didn't warrant reversal of judgement because they were non-prejudicial in light of other compelling evidence presented during trial.

In the case of Nelson, Warden v. O'Neil, Justice Harlan delivered a dissenting opinion. He disagreed with the majority's view that there was no violation of the respondent's Sixth Amendment rights when he was not allowed to cross-examine his own prior testimony from another trial in which he had been acquitted. Justice Harlan argued that this decision contradicted previous rulings by the Supreme Court regarding a defendant’s right to confront witnesses against them and their right to present evidence in their favor. He believed that these principles should apply even if it is one’s own prior statements being used as evidence against them, especially given they were made under oath at an earlier proceeding where perjury penalties applied if false information was provided. Thus, according to him, barring such cross-examination infringed upon fundamental constitutional protections for criminal defendants.