In the case of Don Roper, Superintendent, Potosi Correctional Center v. William Weaver (2006), the U.S Supreme Court addressed a habeas corpus petition from an inmate on death row in Missouri. The petitioner, William Weaver, argued that his constitutional rights were violated because he was not allowed to present mitigating evidence during his sentencing hearing for capital murder. This evidence included information about his troubled upbringing and mental health issues which could have potentially influenced the jury's decision to impose a death sentence. However, the court ruled against him stating that under federal law governing habeas petitions by state prisoners (28 U.S.C § 2254(d)), relief can only be granted if it is found that state court proceedings resulted in decisions contrary to or involving unreasonable application of clearly established Federal law as determined by Supreme Court precedents at time of relevant state-court decision.

In the dissenting opinion for Don Roper, Superintendent, Potosi Correctional Center v. William Weaver (2006), Justice Clarence Thomas disagreed with the majority's decision to grant habeas relief based on ineffective assistance of counsel during sentencing. He argued that Weaver did not meet both prongs of Strickland test - proving that his lawyer's performance was deficient and this deficiency prejudiced his defense. According to him, even if there were deficiencies in counsel’s investigation or presentation at sentencing phase, it is speculative whether a more thorough investigation would have changed outcome given overwhelming evidence of guilt and aggravating factors supporting death penalty. Furthermore, he criticized the Court for its expansive interpretation of AEDPA’s deferential standard which undermines states’ sovereignty in criminal justice matters by allowing federal courts to second-guess state court decisions.