In the case of Holloway et al. v. Arkansas, the U.S Supreme Court ruled that a trial court committed constitutional error when it failed to inquire into potential conflicts of interest among multiple defendants represented by a single attorney. The case involved three co-defendants who were charged with capital felony murder and aggravated robbery in Arkansas state court, all represented by one public defender. One defendant requested separate counsel due to conflicting interests but was denied without further inquiry into possible conflict by the trial judge. All three defendants were convicted and appealed on grounds their Sixth Amendment rights had been violated due to inadequate representation resulting from this conflict of interest. The Supreme Court held that whenever a trial court is aware of an actual or potential conflict involving joint representation, it has an affirmative duty to investigate thoroughly before proceeding with the criminal proceedings; failure to do so constitutes reversible error regardless if prejudice can be shown or not.

In the dissenting opinion for Holloway v. Arkansas, Justice William Brennan Jr., joined by Justices Thurgood Marshall and John Paul Stevens, argued that the trial court's failure to inquire into potential conflicts of interest among defendants represented by a single attorney was an error requiring reversal of convictions. They contended that when a trial judge is aware of a possible conflict of interest in joint representation cases, it becomes their constitutional duty under the Sixth Amendment to investigate further before proceeding with the case. The majority’s decision not to mandate such inquiry would lead to unnecessary retrials and appeals due to avoidable errors at initial trials. The dissenters believed this approach undermined both judicial economy and defendants' right to effective counsel.