A police officer walks in front of the U.S. Supreme Court April 6, 2020 in Washington, DC.

The Supreme Court on Monday ruled that serious criminal convictions reached by non-unanimous juries are unconstitutional, delivering a win for civil rights advocates who traced the connections between split jury convictions to racist state efforts to minimize the role of black jurors.

Justice Neil Gorsuch, writing for a divided court, said there "can be no question" that the Sixth Amendment to the Constitution requires unanimity in state courts. The court had previously held that the requirement only applied at the federal level.

Gorsuch was joined in part by Justices Ruth Bader Ginsburg, Stephen Breyer, Sonia Sotomayor and Brett Kavanaugh. Justice Clarence Thomas agreed with the judgement but didn't join Gorsuch's opinion. Justice Samuel Alito dissented, joined by Chief Justice John Roberts and in part by Justice Elena Kagan.

The decision was widely expected and will have limited impact nationwide, as the only two states that have allowed split jury convictions in recent years are Louisiana and Oregon. Those two states could now face more than a thousand requests for retrials, according to documents they submitted to the justices.

The case was brought by Evangelisto Ramos, who in 2016 was convicted on a murder charge in Louisiana by a vote of 10-2 from a 12-person jury. Ramos has maintained he is innocent of the crime. The case is known as Ramos v. Louisiana, No. 18-5924.

As Ramos' case was working its way through the legal system, a local Louisiana newspaper published an extensive investigation into split juries, finding that they disproportionately harmed black defendants.

Voters in Louisiana outlawed split juries in 2018, for crimes committed in 2019 and beyond, leaving Oregon as the only state where it was still possible to face conviction from a divided panel.

Gorsuch pointed to the racist origins of split juries in his opinion striking them down, writing that courts in both states had "frankly acknowledged" the history.

"Why do Louisiana and Oregon allow nonunanimous convictions? Though it's hard to say why these laws persist, their origins are clear," he wrote.

The Trump appointee cited comments from a committee chairman at the state's 1898 constitutional convention, where Louisiana's non-unanimous verdicts were first endorsed, who said the purpose of the convention was to "establish the supremacy of the white race."

Oregon's rule, Gorsuch wrote, "can be similarly traced to the rise of the Ku Klux Klan" and efforts to dilute the influence of racial, ethnic and religious minorities on Oregon juries.

The court's majority opinion overturned the 1972 case Apodaca v. Oregon, which applied the unanimity requirement to federal juries but not the states. Apodaca was the Supreme Court's last remaining exception to its general rule of applying Bill of Rights protections equally at the state and federal level, Ginsburg remarked in an opinion handed down in February.

Kristen Clarke, president of the Lawyers' Committee for Civil Rights Under Law, said in a statement that the decision "rightfully recognized and condemns the discriminatory motive underlying Louisiana and Oregon's long history of permitting non-unanimous jury verdicts which stood as relics from the Jim Crow era."

"The question remains as to how many prisoners are entitled to new trials as a result of convictions obtained unconstitutionally," she said.

The case prompted a smattering of concurrences from the justices as well as a sharp dissent from Alito, who took issue with Gorsuch's tone and the majority's willingness to cast aside the court's precedent.

"Lowering the bar for overruling our precedents, a badly fractured majority casts aside an important and long-established decision with little regard for the enormous reliance the decision has engendered," Alito wrote.

"To add insult to injury, the Court tars Louisiana and Oregon with the charge of racism for permitting nonunanimous verdicts — even though this Court found such verdicts to be constitutional and even though there are entirely legitimate arguments for allowing them," the George W. Bush appointee wrote.

The decision was handed down online as the justices continue to work at home as a precaution against the coronavirus, which forced the court to close its doors to the public.

The justices are expected to announce decisions in major cases in the coming weeks, including in those related to the Second Amendment, abortion, LGBT rights and an Obama-era immigration program that shields young immigrants known as "Dreamers."