Justice Sotomayor continued in relevant part: At age 29, while in federal prison serving a life sentence for kidnapping and carjacking, Coonce and his codefendant, Charles Michael Hall, attacked and killed Victor Castro Rodriguez, another prisoner. Hall was a decade older than Coonce, with an IQ about 30 points higher. It was Hall who bound, gagged, and blindfolded Castro. Hall consistently asserted that he had killed Castro by standing on his neck and suffocating him. Coonce, however, immediately claimed responsibility for the killing.
A jury convicted Coonce of first-degree murder and murder by a federal prisoner serving a life sentence. See 18 U. S. C. §§1111, 1118. After a penalty-phase hearing, the jury recommended death.1 932 F. 3d 623, 631 (CA8 2019). The jury unanimously found as a mitigating factor that Coonce’s childhood “was marked by chaos, abuse (both physical and sexual), as well as neglect and abandonment.” 932 F. 3d, at 632. Eight jurors also found that Coonce “suffered from mental and emotional impairments from a very young age.” However, on May 27, 2014, in the midst of the penalty-phase proceedings, this Court held that a “rigid rule” disqualifying a defendant from establishing intellectual disability if the defendant “scored a 71 instead of 70 on an IQ test” was unconstitutional. Hall v. Florida, 572 U. S. 701, 724. The next day, Coonce moved for relief under Atkins. He noted that he had scored a 71 on a reliable IQ test and argued that a rigid age-18 onset cutoff, like the 70-IQ cutoff in Hall, was unconstitutional. The District Court denied the motion without a hearing. 932 F. 3d, at 633, 634. The Eighth Circuit affirmed. Id., at 634.
Crimes against prisoners create interesting evidentiary issues for the accused. Normally, evidence of “other crimes” is inadmissible against a defendant. His presence in a prison where the alleged offense was committed lends itself to the clear inferences that he committed a crime and it was serious enough to warrant a prison sentence.