In Duvernay v. United States (1968), the petitioner, Duvernay, was convicted of knowingly transporting a stolen vehicle across state lines in violation of the Dyer Act. He appealed his conviction to the Supreme Court on grounds that he had been denied effective assistance of counsel because his attorney failed to object to certain evidence and testimony during trial. The court rejected this argument, stating that not every error made by a lawyer would constitute ineffective assistance of counsel. To establish such a claim, it must be shown that the errors were so serious as to deprive the defendant of fair trial - one whose result is reliable. In this case, there was no substantial proof showing that any alleged errors affected Duvernay's defense or influenced jury's decision making process significantly enough for him to have been deprived a fair trial.

The dissenting opinion in Duvernay v. United States argued that the majority's decision to uphold the conviction was flawed due to a lack of sufficient evidence. The dissenting justices believed that there were significant issues with how the evidence was collected and presented, which should have resulted in an acquittal for Duvernay. They contended that certain pieces of key evidence had been obtained illegally, thus violating Duvernay’s constitutional rights against unreasonable searches and seizures under Fourth Amendment protections. Furthermore, they expressed concerns about potential bias in witness testimonies used by prosecution during trial proceedings. These factors led them to conclude that upholding such a conviction would set a dangerous precedent for future cases involving similar circumstances.