Cuyler v. Sullivan, 446 U.S. 335 (1980) (U.S. Supreme Court)
Cuyler v. Sullivan is a cornerstone Sixth Amendment case that sets the modern framework for evaluating attorney conflicts of interest, especially those arising from multiple representation of co-defendants.
When a defendant is represented by counsel who also represents codefendants in related prosecutions and the defendant raised no conflict objection at trial, what must the defendant show to establish a Sixth Amendment violation based on a conflict of interest, and under what circumstances does a trial court have a constitutional duty to inquire into counsel's potential conflict?
A defendant who did not object to multiple representation at trial must demonstrate that an actual conflict of interest adversely affected his lawyer's performance to establish a Sixth Amendment violation; a mere possibility of conflict is insufficient. If the defendant makes this showing, prejudice is presumed and he need not demonstrate a reasonable probability of a different outcome. A trial court has a constitutional duty to inquire into potential conflicts only when it knows or reasonably should know that a particular conflict exists. The Sixth Amendment right to conflict-free counsel applies whether counsel is appointed or privately retained.
The Supreme Court held that, absent a timely objection, a defendant alleging a Sixth Amendment violation due to multiple representation must show that an actual conflict of interest adversely affected counsel's performance; potential or speculative conflicts do not suffice. The trial court has no duty to inquire into conflicts sua sponte unless it knows or reasonably should know of a particular conflict. The Court reversed the judgment of the Court of Appeals and remanded for application of this standard.
Cuyler v. Sullivan sets the controlling standard for conflict-of-interest claims where no timely objection was made: a defendant must show an actual conflict that adversely affected counsel's performance, after which prejudice is presumed. It cabin's Holloway's automatic-reversal rule to cases with a timely objection and a trial court's failure to act, and it later interfaces with Strickland v. Washington by providing a distinct, conflict-specific presumption of prejudice once adverse effect is proven. For law students, Cuyler is a must-know case on the doctrinal triad governing conflicts (Holloway–Cuyler–Mickens), on the trial court's limited duty to inquire, and on how to plead and prove "adverse effect" distinct from outcome-determinative prejudice.