WASHINGTON — The terse Supreme Court rulings arrived in the evening, in time to allow an execution later that night. There were three rulings in the last month or so, at 5:52 p.m., at 7:01 p.m. and at 10:13 p.m. They were bland and formulaic, saying only that the court had denied an “application for stay of execution of sentence of death.” The inmates who had filed the applications were put to death within hours.

In all three cases, only one member of the court bothered to write an opinion, to give a hint about what was at stake. That was Justice Sonia Sotomayor, who maintains a sort of vigil in the capital cases other justices treat as routine. She described shortcomings in the trials the inmates had received and oddities in the laws the courts below had applied.

“She’s bearing witness,” said Douglas A. Berman, a law professor at Ohio State University.

On Wednesday, for instance, she wrote about the trial of Robert Sparks, in Texas in 2008. One of the bailiffs had worn a black tie embroidered with a white syringe, later admitting that he wanted to express his support for the death penalty.

“That an officer of the court conducted himself in such a manner is deeply troubling,” Justice Sotomayor wrote. But, with seeming reluctance, she said the Supreme Court was right not to intervene in the case. A lower court considering a challenge to Mr. Sparks’s death sentence, she wrote, “did not find sufficient evidence to conclude that the jury saw the tie.”