Three Justices join Justice Breyer questioning how Arizona's death penalty system operates

Many month ago, as highlighted here, the cert petition in Hidalgo v. Arizona generated considerable attention.  That matter ended today when the petition for a writ of certiorari was denied, along with this lengthy statement by Justice Breyer joined by Justices Ginsburg, Sotomayor and Kagan. I was expecting some Justices to say something really notable after all this build up, by the statement ends this way:

Although, in my view, the Arizona Supreme Court misapplied our precedent, I agree with the Court’s decision today to deny certiorari. In support of his Eighth Amendment challenge, the petitioner points to empirical evidence about Arizona’s capital sentence system that suggests about 98% of first-degree murder defendants in Arizona were eligible for the death penalty.  That evidence is unrebutted. It points to a possible constitutional problem.  And it was assumed to be true by the state courts below. Evidence of this kind warrants careful attention and evaluation. However, in this case, the opportunity to develop the record through an evidentiary hearing was denied. As a result, the record as it has come to us is limited and largely unexamined by experts and the courtsbelow in the first instance. We do not have evidence, for instance, as to the nature of the 866 cases (perhaps they implicate only a small number of aggravating factors).  Nor has it been fully explained whether and to what extent an empirical study would be relevant to resolving the constitutional question presented.  Capital defendantsmay have the opportunity to fully develop a record with the kind of empirical evidence that the petitioner points to here. And the issue presented in this petition will be better suited for certiorari with such a record.

Meh.