Over at Scotusblog, Lyle Denniston provides the context:
Landrigan was sentenced to death for a 1989 murder in Phoenix after he had escaped from an Oklahoma prison, where he was serving a sentence for second-degree murder. As the scheduled execution date of October 26 approached, Landrigan (after losing in a challenge in state court) filed a federal civil rights lawsuit, contending that the method of his execution would violate his Eighth Amendment right to be free from cruel and unusual punishment and his Fourteenth Amendment right to due process. The Eighth Amendment claim was based on an argument that the state would be using sodium thiopental — one of the drugs in the execution protocol — that had not been shown to be safe in terms of avoiding needless pain. The due process claim was based on the argument that the state had refused to disclose to him where it got that drug and whether it had been approved by the Food and Drug Administration as safe.
U.S. District Judge Roslyn Silver of Phoenix, after several preliminary disputes over the drug’s source, on Monday temporarily delayed Landrigan’s execution scheduled for the following morning, in order to inquire further into the dispute. A panel of the Ninth Circuit Court on Tuesday turned down the state’s request to lift Silver’s order. Because the state had not provided the information that Judge Silver had sought, the Circuit Court panel said, it could not make an informed decision on the dispute. The state then asked Justice Kennedy to lift Silver’s order, and Kennedy referred the plea to the full Court.
The Supreme Court vacated the District Judge’s order enjoining the execution in a short order available here. The vote was 5-4, with Ginsburg, Breyer, Sotomayor, and Kagan dissenting. From the order, which would have been likely authored by Justice Kennedy (as the Circuit Justice):
There is no evidence in the record to suggest that the drug obtained from a foreign source is unsafe. The district court granted the restraining order because it was left to speculate as to the risk of harm. See Order Granting Motion for a Temporary Restraining Order in Landrigan v. Brewer, No. CV–10–02246–PHX–ROS (D Ariz.), Doc. 21, p. 15 (“[T]he Court is left to speculate. . .whether the non-FDA approved drug will cause pain and suffering.”). But speculation cannot substitute for evidence that the use of the drug is “‘sure or very likely to cause serious illness and needless suffering.’” Baze v. Rees, 553 U. S. 35, 50 (2008) (quoting Helling v. McKinney, 509 U. S. 25, 33 (1993)).