Final answer:
The U.S. Supreme Court case Furman v. Georgia invalidated the death penalty for many offenders in 1972, establishing that its inconsistent application was unconstitutional. This led to a temporary nationwide halt of executions until the Gregg v. Georgia decision. Further cases have continued to restrict the death penalty's use for certain populations and crimes.
Step-by-step explanation:
Invalidating the Death Penalty for Offenders
The U.S. Supreme Court case that invalidated the death penalty for over six hundred offenders on death row at the time was Furman v. Georgia, 408 U.S. 238 (1972). This landmark decision held that the arbitrary and inconsistent imposition of the death penalty violates the Eighth and Fourteenth Amendments and constitutes cruel and unusual punishment. The result was a de facto nationwide moratorium on executions until the court's decision in Gregg v. Georgia (1976), which upheld Georgia's new death penalty statute and ended the moratorium.
Following cases like Atkins v. Virginia in 2002 and Roper v. Simmons in 2005, the Supreme Court ruled that executions of individuals with intellectual disabilities and juvenile offenders were unconstitutional. Similarly, Kennedy v. Louisiana (2008) determined that the death penalty is unconstitutional in cases not involving murder or crimes against the state. These decisions reflect the Supreme Court's ongoing efforts to narrow the application of the death penalty.