Final answer:
A certificate of appealability is required for a death penalty litigant to appeal a federal court's decision in habeas corpus proceedings when there is a substantial showing of the denial of a constitutional right. The Supreme Court's rulings continue to define the scope of the death penalty, such as prohibiting the execution of the intellectually disabled and juveniles, underscoring the evolving nature of capital punishment laws.
Step-by-step explanation:
A certificate of appealability must be obtained by a death penalty litigant when they wish to appeal a federal district court's final order in a habeas corpus proceeding. The United States federal judicial system requires this certificate as a means to demonstrate that the case involves a matter in which the litigant has made a substantial showing of the denial of a constitutional right. Notably, the Supreme Court has the authority to further interpret laws related to the death penalty and has made several decisions that refine its application, for example, ruling out the execution of individuals with intellectual disabilities or those who were minors at the time of the crime.
Significant rulings have shaped the landscape of death penalty litigation, including cases such as Atkins v. Virginia, which established the unconstitutionality of executing individuals with intellectual disabilities, and Roper v. Simmons which held that executing individuals who were under 18 at the time of their crime is unconstitutional. The jurisprudence continues to evolve, and as new cases arise, the need for judicial interpretation persists.
The process of obtaining a certificate of appealability is crucial for a death penalty litigant to advance an appeal, and the criteria for granting a certificate focus on potential constitutional violations that might affect the legitimacy of the conviction or sentence.