Which case established a precedent against the death penalty for individuals who are mentally incompetent?

Atkins v. Virginia set a significant precedent regarding the death penalty and individuals who are mentally incompetent. The Supreme Court ruled that executing individuals who are intellectually disabled is unconstitutional as it violates the Eighth Amendment's prohibition against cruel and unusual punishment. The Court's decision was based on the understanding that individuals with intellectual disabilities have reduced culpability, which makes the death penalty an inappropriate and disproportionate form of punishment for them.

This ruling recognized the ethical and moral considerations surrounding the treatment of individuals who may not fully grasp the consequences of their actions or the nature of the legal proceedings against them. The decision in Atkins v. Virginia emphasizes the importance of individual mental capacity when determining punishment, reiterating that humane treatment should extend to all individuals, regardless of their mental states.

This case differs significantly from the others listed, as Roper v. Simmons addresses juvenile offenders and the death penalty, Tennessee v. Garner deals with the use of deadly force by law enforcement, and Miranda v. Arizona pertains to the rights of individuals in police custody.