In the United States v. Nobles case of 1974, the Supreme Court ruled in favor of the government, stating that a defense investigator's report could be used for cross-examination purposes if it was introduced as evidence by the defendant during trial. The case arose when Robert Allen Nobles was convicted of bank robbery and his attorney sought to introduce an investigator’s report into evidence to impeach a prosecution witness' credibility. However, he refused to share all parts of this report with prosecutors which led them to request its complete disclosure or exclusion from evidence altogether. The trial court sided with prosecutors and excluded it entirely due to non-disclosure. On appeal, Nobles argued that this violated his Sixth Amendment right (right-to-counsel clause). But the Supreme Court disagreed holding that since defendants are not allowed under law to present only favorable portions while withholding unfavorable ones from their own reports; full disclosure is necessary once they decide introducing such reports into evidence.

In the dissenting opinion for United States v. Nobles, Justice William O. Douglas argued that the majority's decision to allow a defense investigator's report as evidence violated the defendant’s Sixth Amendment right to counsel. He contended that this ruling could potentially deter defendants from hiring investigators due to fear of their findings being used against them in court, thus undermining their ability to build an effective defense strategy. Furthermore, he expressed concern over potential abuse by prosecutors who might use such rulings as a means of gaining access to privileged information about a defendant’s case preparation and legal strategies.