In its unanimous opinion, the court expressed no view on the constitutionality either of lethal injection in general or of the specific procedures and combination of chemicals that a Florida inmate, Clarence E. Hill, and numerous others around the country have recently challenged in federal court.
The justices addressed themselves solely to the procedural route that such lawsuits must take, and chose the route that is by far the more inmate-friendly from the two options that the case presented.
Nonetheless, it was the tight focus of the case, an appeal by Mr. Hill of a ruling by the federal appeals court in Atlanta, that probably enabled the justices to maintain their unanimity. It remains to be seen how they would rule on the underlying constitutional question of whether the disputed lethal injection method violates the Eighth Amendment's prohibition on cruel and unusual punishment.
Just three weeks ago the court turned down, without comment, a case from Tennessee, Abdur'Rahman v. Bredesen, that presented that issue directly. The justices have also permitted several executions to be carried out by lethal injection, without intervening, while the Florida case was pending.
Federal courts around the country have begun wrestling with the issue, which opponents of the death penalty have brought to the fore in recent months on the basis of a report last year in a British medical journal, The Lancet.
The focus of concern is two of the three chemicals that make up the lethal cocktail used by most states. One is sodium pentothal, an anesthetic, which Mr. Hill argues in his lawsuit is insufficient to make the procedure painless.
The second is pancuronium bromide, which causes muscle paralysis but does not block pain or interfere with consciousness. Studies indicate that while inmates who receive this drug look calm and peaceful as the third chemical, potassium chloride, is administered to stop the heart, they can actually feel intense pain without being able to express themselves.
Mr. Hill's suit maintains that Florida's procedure for administering these three drugs presents a "foreseeable risk of gratuitous and unnecessary pain."
Having been convicted in 1983 of killing a police officer, Mr. Hill had long since run through the ordinary appeals process by the time he filed his suit in state court last December, with his execution set for Jan. 24. After the Florida courts threw the case out, and with the clock running, he turned to federal court with an equally poor result. He was strapped to a gurney, intravenous lines to administer the chemicals already inserted, when Justice Anthony M. Kennedy issued a stay nearly five months ago.
The case was filed under the Civil Rights Act of 1871, a Reconstruction-era law usually referred to as Section 1983, for its placement in the compilation of federal statutes. Section 1983 permits suits against government officials for violation of rights guaranteed by the Constitution or federal laws.
The lower federal courts dismissed the suit, however, on the ground that the only way for an inmate to challenge the method by which he is to be executed is through a petition for a writ of habeas corpus.
While such a petition, like a Section 1983 case, can raise constitutional issues, there is a major problem: both Congress and the Supreme Court have placed high hurdles in the path of inmates seeking habeas corpus. For example, it is almost impossible for an inmate who has filed an initial habeas corpus petition to receive permission to file another one, and Mr. Hill had filed one years earlier. Declaring that his Section 1983 suit was the equivalent of a new habeas corpus petition, the lower courts declared that it was barred.
In his opinion for the Supreme Court on Monday, Justice Kennedy said this analysis was mistaken. He said that while a habeas corpus petition was the only way to challenge the constitutionality of a sentence, Mr. Hill was challenging not his "lethal injection sentence as a general matter," but only the way in which the sentence was to be carried out.
Justice Kennedy noted that if Mr. Hill eventually won his case, Florida would not be barred from executing him by lethal injection but would simply have to use a different protocol.
Mr. Hill is now entitled to pursue his Section 1983 suit in the Federal District Court in Tallahassee, where he filed it in January.
When the case, Hill v. McDonough, No. 05-8794, was argued in April, there was considerable debate over whether Mr. Hill should be required to demonstrate his sincerity by specifying a method acceptable to him. Chief Justice John G. Roberts Jr. was among the justices who appeared to endorse such a requirement. But the justices evidently decided to set that argument aside for now, for the sake of unanimity.
The precedent for the ruling on Monday was a 2004 decision in which the court permitted an inmate to use Section 1983 to challenge a surgical procedure that Alabama proposed to use to gain access to his collapsed veins for the purpose of administering a lethal injection.