NORMAN, OKLA. — A defense attorney, Lisa McCalmont, was well-known nationally as an outspoken critic of lethal injection and amassed a trove of information about problems with the three-drug cocktail that is at the very center of a case the Supreme Court will hear early next year.

Colleagues say McCalmont, 49, was looking forward to the Supreme Court case as a momentous event in her career.

But then, last week, she hanged herself at her home in Norman — a suicide that stunned and baffled some of those who knew her.

“She seemed like she was on top of the world,” Dr. William Kinsinger, an Oklahoma City anesthesiologist who worked with McCalmont on a capital case, said. “I’m absolutely dumbfounded.”

Her husband, Craig Dixon, a geophysicist, would not discuss what might have troubled his wife. She left no suicide note.

At the time of her death, she was a consultant to the Death Penalty Clinic at the law school at the University of California at Berkeley, and worked passionately to save the lives of death row inmates. She advised attorneys across the country who were working on challenges to lethal injection.

McCalmont was not directly involved in the Kentucky case before the Supreme Court, in which two condemned men claim lethal injection amounts to cruel and unusual punishment in violation of the Eighth Amendment.

But colleagues said she helped lay the groundwork for similar challenges in other jurisdictions. She argued that if the drugs were not properly administered, the condemned could suffer pain without being able to cry out.

“We wouldn’t be where we are today with lethal injection cases if it were not for her,” Ty Alper, a colleague of McCalmont’s at the Death Penalty Clinic, said. “In large part due to the work of lawyers like Lisa, lawyers in every death penalty case are challenging the method of lethal injection in their cases.”

In agreeing to hear the case, the Supreme Court appears to have put a halt to executions in America for now.