Cone v. Bell, 556 U.S. 449 (2009), was a case in which the United States Supreme Court held that a defendant was entitled to a hearing to determine whether prosecutors in his 1982 death penalty trial violated his right to due process by withholding exculpatory evidence.

[1] The defendant, Gary Cone, filed a petition for postconviction relief from a 1982 death sentence in which he argued that prosecutors violated his rights to due process under the Fourteenth Amendment by withholding police reports and witness statements that potentially could have shown that his drug addiction affected his behavior.

[4] In 1982, Gary Cone was convicted and sentenced to death for a crime spree that included the robbery of a jewelry store, a police pursuit, and the murder of an elderly couple.

[6] According to one expert, Cone's long-term drug abuse caused hallucinations and paranoia that "affected respondent's mental capacity and ability to obey the law.

[23] Justice John Paul Stevens wrote a dissenting opinion in which he argued that Cone's attorney "entirely fail[ed] to subject the prosecution's case to meaningful adversarial testing.

[27] In a 2007 opinion, the Sixth Circuit reconsidered whether the prosecution violated Cone's rights to due process under the Fourteenth Amendment[28] by withholding police reports and witness statements that potentially could have corroborated his claims about the effects of his drug use.

"[32] Justice Stevens noted that "the quantity and the quality of the suppressed evidence lends support to Cone’s position at trial that he habitually used excessive amounts of drugs, that his addiction affected his behavior during his crime spree, and that the State’s arguments to the contrary were false and misleading.