Could people facing the death penalty lose the right to tell juries their life stories?

On a March evening last year, death penalty lawyers, scholars, and trained investigators gathered in an Atlanta hotel room to celebrate Wiggins v. Smith. The 20-year-old Supreme Court decision declared that defense lawyers in death penalty cases must thoroughly investigate the lives of those facing execution for evidence that might see them spared.

The court held that lawyers needed to explore a defendant's medical, educational, family, and social histories, as well as religious and cultural influences, and any prior time spent behind bars. Defendants whose lawyers failed to do so, the court ruled, could rightly claim they were victims of inadequate counsel, deprived of a basic constitutional right.

Amid the presentations and discussions, there came a question that stirred alarm among the scores of people in attendance.

Given the conservative majority on the court, was there reason to worry about the implications of a 2022 Supreme Court decision by Justice Clarence Thomas?

Thomas had denied the appeal of the man convicted and sentenced to death for his role in the 2013 Boston Marathon bombing. In doing so, he had once again telegraphed his disdain for the long line of Supreme Court cases—Wiggins included—that established the constitutional right for death penalty defendants to present mitigating evidence that might move a jury to grant them mercy.

Forcing a smile, Donald B. Verrilli Jr., the former U.S. solicitor general and the man who had successfully argued the Wiggins case before the Supreme Court, indicated it was hard to say what level of fear was warranted, but he did not dismiss it. The unease in the room was palpable.

People needed to be prepared, one veteran death penalty lawyer said.

Since the U.S. Supreme Court's decision in 1976 that allowed the death penalty's return, its justices have wrestled with arguments over who could be executed and how the life-and death-decisions in capital cases are made.

In Ford v. Wainwright, the court held in 1986 that "insane" people could not be sentenced to die; Atkins v. Virginia in 2002 barred the execution of people with mental disabilities; the 2005 case Roper v. Simmons ruled out executing those who committed their crimes when they were under the age of 18.

For those eligible for the death penalty, the court has repeatedly defined and expanded the requirement that mitigating factors—including, in its language, the "diverse frailties of humankind"—must be considered during the sentencing phase of capital cases.

The 1978 decision in Lockett v. Ohio said judges and juries were entitled to hear any aspects of a defendant's life that might lead to a decision sparing them. In Skipper v. South Carolina, the court said even a defendant's conduct after their arrest and conviction—model behavior, educational accomplishments, service to others—could be weighed by death penalty juries.

All along, though, any number of conservative judges, Antonin Scalia and Thomas among them, have raised concerns about the use of mitigating factors.

Scalia, in particular, railed against the questionable relevance of what a jury could be told about a defendant's history, and outright pledged never to honor the court's precedents supporting the use of such evidence. In the 1990 case Walton v. Arizona, he unleashed his most withering critique.

"Our cases proudly announce that the Constitution effectively prohibits the States from excluding from the sentencing decision any aspect of a defendant's character or record, or any circumstance surrounding the crime: that the defendant had a poor and deprived childhood, or that he had a rich and spoiled childhood; that he had a great love for the victim's race, or that he had a pathological hatred for the victim's race; that he has limited mental capacity, or that he has a brilliant mind which can make a great contribution to society; that he was kind to his mother, or that he despised his mother. Whatever evidence bearing on the crime or the criminal the defense wishes to introduce as rendering the defendant less deserving of the death penalty must be admitted into evidence and considered by the sentencer."

No basis for such considerations, he argued, could be found in the Constitution. The court, he wrote, had properly held that the application of the death penalty could not be random, only to then, through the consideration of a differing and near limitless variety of mitigating factors, make just such randomness all the more likely. Scalia encouraged the court to abandon its prior rulings.

Certainly, today's Supreme Court has shown a willingness to revisit long-established doctrines—in cases involving abortion, voting rights, gun control, and affirmative action.

And so when Thomas issued his decision in the Boston Marathon bombing case, some in the capital defense community took notice. Lawyers for the convicted bomber had argued that the jury that sentenced him to die had been denied the chance to hear his argument that he'd been manipulated into the terrorist act by his older, domineering, and violent brother.

Thomas was not persuaded, and upheld the trial court judge's ruling that there was insufficient admissible evidence the bomber's older brother had a history of prior violence or had effectively coerced him into carrying out the plot. Thomas noted that the court's decisions over the years had allowed states some ability to limit what they regarded as irrelevant mitigating evidence.

Thomas then took the step of adding a footnote to his decision highlighting the fact that "critics," as he put it, had long argued the Supreme Court had repeatedly erred in finding a constitutional basis for the use of mitigating factors in death penalty cases.

For some, the modest but pointed footnote seemed to be a forewarning. One capital defense lawyer said such footnotes are often used as "signals" by justices, a way of suggesting they'd be open to revisiting an issue. The lawyer said there were those in the death penalty defense community who were now on guard to see if there might be a case making its way through the courts across the country that the justices could one day agree to hear.

Lee Kovarsky, a professor at the University of Texas School of Law, said throughout his time on the bench, Thomas had been hostile to all sorts of the court's rulings that placed limits on the death penalty. He said Thomas would be happy to "gut" the court's prior rulings on mitigating evidence, and likely could count on Samuel Alito and Neil Gorsuch to join him.

But Kovarsky doubted there would be the required five justices willing to do so any time soon. Many states have moved away from capital punishment. That said, Kovarsky was confident there were solicitors general in certain states working to put a case before the nation's top court.

Kent Scheidegger has spent years arguing and agitating for the Supreme Court to limit or abandon its prior decisions concerning mitigating evidence in capital cases. Scheidegger is the legal director of the Criminal Justice Legal Foundation, a conservative nonprofit organization that says it works to "assure that people guilty of committing crimes receive swift and certain punishment in an orderly and constitutional manner."

In 2022, Scheidegger filed a "friend of the court" brief with the Supreme Court that attacked the weight given to mitigating factors in death penalty cases, and called for overturning Lockett v. Ohio—the case that first established the use of such evidence. He invoked the Supreme Court's decisions over the last several years reversing established precedents, the right to abortion among them.

"Lockett meets the criteria for overruling laid out in recent decisions of this Court," he wrote. "It was egregiously wrong and poorly reasoned."

In an interview, Scheidegger made the argument Scalia had years ago: Executing people randomly was wrong—but allowing, as he put it, "every scrap of mitigation," produced just such randomness.

"If you require the consideration of evidence purported to be mitigating, but with little relevance to actual culpability, then results are going to vary," he said.