Oklahoma City criminal attorney David Slane has been working on an appeal in one of his sexual assault cases for years — arguing that his client, a Native American, can’t be legally prosecuted by the state of Oklahoma because the crime occurred on what has historically been Indian land.

On Thursday, his argument got a boost after a landmark decision by the Supreme Court, which ruled in 5-to-4 vote that much of eastern Oklahoma remains part of an Indian reservation. The state has no criminal jurisdiction over the land — home to nearly 775,000 people and portions of its second-largest city, Tulsa — because Congress never formally dissolved the reservation’s boundaries when Oklahoma became a state in 1907.

The Supreme Court’s historic ruling reverberated through the state Friday — with government officials, legal experts and activists saying the case will have complicated legal ramifications in tribal disputes for decades to come.

Experts said that Native Americans arrested in major crimes on Indian land belonging to the Muscogee (Creek) Nation must now be prosecuted federally, and dozens of convicted criminals may seek to overturn their convictions.

“It’s going to have a far-reaching effect,” Slane said. “You’re going to have other Indians making the same argument in federal court — throughout Oklahoma and throughout the nation.”

Critics, attorneys like Slane and other legal experts argue that the ruling could also ultimately impact civil matters in the state, such as taxation, zoning or custody battles.

“People may still be in a bit of a shock trying to wrap their minds around the implications of this,” said Lindsay Robertson of the University of Oklahoma’s Center for the Study of American Indian Law and Policy. “People are thinking of who has the power to tax, who is the zoning authority now, and if I’m going to sue somebody, do I file in tribal court or state court?”

Native American leaders sought to calm such fears. They pointed to a statement released just after the ruling by the state’s attorney general, Mike Hunter, and the five impacted tribes — Creek, Cherokee, Chickasaw, Choctaw and Seminole — announcing that the two sides have made “substantial progress toward an agreement” to be submitted to Congress and the Justice Department in the coming months that would put in place a “framework of shared jurisdiction” going forward.

“This is a monumental decision, but it’s important to relay to citizens of the broader public that doesn’t mean the sky is falling,” said Chuck Hoskin Jr., the chief of the Cherokee Nation, the largest tribe in the United States. “There’s no immediate impact beyond criminal jurisdiction. It does raise questions, but they are not insurmountable. There shouldn’t be any instability or uncertainty in our court or regulatory system. These are things that can be worked out.”

The state also appeared to be looking to Congress to act in the wake of the ruling, which held that Congress, not the courts, has the authority to modify treaty agreements and change reservation boundaries.

Gov. Kevin Stitt (R) said Thursday that state officials were still trying to determine whether the ruling affects only the prosecution of crimes or went beyond that scope.

“All those questions nobody really knows at this point,” Stitt said. “This is a federal issue. This is something Congress needs to address, to put some parameters to see exactly how we’re supposed to deal with this.”

The ruling hinged on the case of an Oklahoma man, Jimcy McGirt, a Native American convicted and sentenced to life in prison after raping a 4-year-old child in 1996. McGirt’s attorneys had argued that the state did not have the authority to prosecute him because the crime occurred on the Creek reservation, established during a treaty with the federal government after the Native Americans were forcibly moved to “Indian Country” in 1833.

“Today we are asked whether the land these treaties promised remains an Indian reservation for purposes of federal criminal law,” Justice Neil M. Gorsuch, a Trump-appointed conservative, wrote in the majority opinion, which evoked broken promises the U.S. government made to Native Americans as far back as the Trail of Tears. “Because Congress has not said otherwise, we hold the government to its word.”

Native Americans and their allies have celebrated the ruling with the hashtag #NativeLivesMatter and said that they hoped future court decisions would be shaped by the country’s current period of self-reflection on race and the moves to right historic wrongs.

“The country has more of an appetite to have a conversation on institutional and systemic racism, and when state and local governments infringe on tribal sovereignty, that’s racism,” said Aila Hoss, a University of Tulsa law professor and an expert on Indian law.

Hoss said the primary impact of the court’s decision would be on Indian defendants convicted of major crimes by the state, raising the question of whether the case should be retried in federal court.

While the state had argued that could mean hundreds of cases being overturned, a review by the Atlantic came to a different conclusion. An analysis of about 300 of the 1,887 Native Americans in prison in Oklahoma at the end of last year for offenses on tribal territory showed that only an estimated 10 percent would qualify for a new trial.

Concerns over the ruling’s reach beyond criminal prosecution were largely exaggerated, Hoss argued, because tribes have very limited civil jurisdiction over nonmembers.

Yet in the dissenting opinion, Chief Justice John G. Roberts Jr. warned: “Across this vast area, the State’s ability to prosecute serious crimes will be hobbled and decades of past convictions could well be thrown out. On top of that, the Court has profoundly destabilized the governance of eastern Oklahoma.

“The decision today creates significant uncertainty for the State’s continuing authority over any area that touches Indian affairs, ranging from zoning and taxation to family and environmental law.”

Dewey Bartlett, a former Tulsa mayor who runs his family oil business, said he thinks many Oklahoma business owners in oil and gas or ranching may fear that the victory will embolden tribes to take future legal steps to limit water or mineral rights or to avoid state regulators.

“I don’t think people in Tulsa woke up today thinking they live on an Indian reservation, but eventually, they could become concerned that position could be made,” Bartlett said. “It’s very worrisome.”