Oregon’s decades-long practice of allowing split verdicts to convict felony defendants came to an end Monday when the U.S. Supreme Court found such jury systems to be unconstitutional in a ruling that could invalidate hundreds of criminal convictions in the state.

The 6-3 vote overturns an earlier decision by the nation’s high court nearly 50 years ago that allowed two states, Oregon and Louisiana, to continue the practice, which critics say had its roots in racial, ethnic and religious bigotry.

The case centered on a Louisiana man, Evangelisto Ramos, who was convicted by a 10-2 jury in 2016 of killing a woman in New Orleans. Louisiana later amended its constitution to prohibit split jury convictions, but only in cases prosecuted after 2018.

Justice Neil Gorsuch wrote in the majority opinion for Ramos v. Louisiana that nonunanimous juries are inconsistent with the constitutional right to a jury trial.

“Wherever we might look to determine what the term ‘trial by an impartial jury trial’ meant at the time of the Sixth Amendment’s adoption — whether it’s the common law, state practices in the founding era, or opinions and treatises written soon afterward — the answer is unmistakable,” Gorsuch wrote. “A jury must reach an unanimous verdict in order to convict.”

Five justices from across the court’s ideological spectrum — Clarence Thomas, Ruth Bader Ginsburg, Stephen Breyer, Sonia Sotomayor and Brett Kavanaugh — joined the ruling, which also said the split jury laws were based in discrimination.

"Courts in both Louisiana and Oregon have frankly acknowledged that race was a motivating factor in the adoption of their states’ respective non-unanimity rules,” wrote Gorsuch.

In a dissent, Justice Samuel Alito warned that the decision could trigger “a potential tsunami of litigation on the jury unanimity issue. At a minimum, all defendants whose cases are still on direct appeal will presumably be entitled to a new trial if they were convicted by a less-than-unanimous verdict and preserved the issue in the trial court.

“And at least in Oregon, even if no objection was voiced at trial, defendants may be able to challenge their convictions based on plain error,” Alito argued. Chief Justice John Roberts and Justice Elena Kagan also dissented from the majority opinion.

Oregon’s Department of Justice last fall had sounded a similar note of caution in a brief filed with the Supreme Court, claiming the state’s court and criminal justice systems would be overwhelmed by a “staggering” number of claims to revisit nonunanimous verdicts and potential retrials.

Ellen Rosenblum, the state’s attorney general, at the time said defense lawyers had already hundreds of cases pending appeal. On Monday, the attorney general said her office had been expecting the justices’ ruling in striking down nonunanimous juries.

“We’re well-prepared to address its significant consequences for Oregon’s justice system," Rosenblum said in a statement. "We have been working closely for months with our appellate courts and with the leadership of the criminal defense bar to plan our case review and the judicial process that will ensue.”

Rosenblum’s statement didn’t provide any details for those case review plans.

Todd Sprague, a spokesman with the Oregon Judicial Department, said the agency is working with the Oregon Department of Justice and Office of Public Defense Services to identify which convictions on appeal could be reversed quickly and returned to trial court. Other cases could take weeks or months to determine whether a reversal is warranted.

Sprague said the Oregon Supreme Court is currently holding 74 petitions for review in criminal appeal cases that might be affected by the high court’s ruling. It’s less clear how many of the 2,900 criminal cases before the state Court of Appeals could be affected, according to Sprague.

Others also have been awaiting the decision. For instance, lawyers for Michael Sperou, a 69-year-old Portland pastor twice convicted of sexually abusing a former member as a young child, told the court in January they expected to be seeking another trial because the jury had returned an 11-1 verdict.

Oregon was the only state in the country that allowed juries in most felony cases — aside from murder — to convict defendants with a 10-2 or 11-1 vote. Federal courts and all other states require a unanimous verdict for crimes such as manslaughter, rape and arson.

In 2018, voters in Louisiana rejected their system of split-verdict convictions. The state also had allowed split verdicts in murder cases. A relic of the Jim Crow era, the law had been adopted during Louisiana’s 1898 constitutional convention to diminish the influence of black jurors upon verdicts, scholars say.

Oregon voters in 1934 approved a constitutional amendment creating the state’s own nonunanimous jury system. Legal scholars and reform advocates have argued Oregon’s law at the time aimed to silence immigrants and religious minorities who served on juries.

The Supreme Court upheld Oregon and Louisiana’s jury laws in 1972, ruling in Apodca v. Oregon that jury verdicts in federal felony trials must be unanimous, but leaving the door open to states having a different standard. It declined to hear cases challenging Oregon’s split jury verdicts as recently as 2009.

A movement to end nonunanimous verdicts in Oregon began to build in 2017 after Aliza Kaplan, a Lewis & Clark College law professor, published an influential article in the Oregon Law Review.

According to Kaplan, it was a sensational, highly publicized murder trial involving a Jewish suspect — and a lone juror’s refusal to convict him — that prompted Oregon voters to amend the state’s constitution. The article also argued in detail how nonunanimous juries have undermined the state’s criminal justice system and continued to serve as a vestige of Oregon’s less-tolerant past.

Kaplan’s analysis quickly captured the attention of criminal justice reformers, state lawmakers and even some judges. But efforts to overturn nonunanimous juries fizzled.

Oregon’s powerful district attorneys association said in early 2018 it would lead a ballot initiative fight to repeal the state’s split verdict jury system. It then abandoned its plans only weeks later.

The Oregon Legislature last year also came up short. After House lawmakers unanimously approved a bill that would ask voters to overturn the state’s jury system, the measure was left to languish in the Senate.

“After 85 years, the U.S. Supreme Court’s ruling in Ramos v. Louisiana today has finally ended an unjust rule with a shameful past in Oregon," Kaplan said. “Now Oregon will be able to join the rest of the country.”

-- Shane Dixon Kavanaugh; 503-294-7632

Email at skavanaugh@oregonian.com

Follow on Twitter @shanedkavanaugh

Subscribe to Oregonian/OregonLive newsletters and podcasts for the latest news and top stories