When the U.S. Army Corps of Engineers said last month that the 9,000-year-old skeleton known as Kennewick Man, or the Ancient One, was ancestral to modern-day Native Americans, it looked like the end of a 20-year-old dispute between local Native American tribes who want to lay the bones to rest and scientists who believe they should be kept available for study.

But a potentially sticky procedural step remains: Under federal law the tribes must still prove they have a “cultural affiliation” with the Ancient One, who was found on a bank of the Columbia River near Kennewick, Wash., in 1996. Four tribal nations and one federally recognized band—the Yakama Nation, Nez Perce Tribe and the Wanapum Band, along with the Colville and Umatilla confederations—are now making a joint claim to have the bones turned over to them.

The question of custody also seemed to have been settled in 2004, when the tribes lost a U.S. Court of Appeals case to a group of scientists who argued that the bones belonged to a member of a group of early migrants to North America who were not related to modern Native Americans. The scientists won the right to analyze the skeleton.

That decision was a painful loss for the tribes. But last year a study of the Ancient One’s DNA, led by Eske Willerslev of the Natural History Museum of Denmark, showed that the Ancient One was clearly an ancestor of modern-day Native Americans, and may also be particularly closely related to the tribes who tried to claim custody of his remains. The Corps confirmed Willerslev’s results and is now revisiting the question of whether the tribes should gain custody of the remains under the Native American Graves Protection and Repatriation Act (NAGPRA).

Cultural affiliation means, in essence, which tribal culture most closely matches the one in which the Ancient One lived—a far different matter from a biological connection, which can be physically established using DNA. Affiliation is obviously difficult to determine when cultures have had 9,000 years to change. Sometimes artifacts buried with human remains can provide cultural clues. And although none were found with the Ancient One, there was a stone spear tip or arrowhead embedded in his hip—a wound he survived but one that probably caused severe pain throughout his life.

Biological and archaeological grounds are just two of the nine kinds of evidence that could be used under NAGPRA to determine his cultural affiliation. The others are geographical, kinship, oral historical, anthropological, linguistic, folkloric and historical.

Gail Celmer, an archaeologist for the Corps’s Northwestern Division, says she and her colleagues hope to complete the process of determining cultural affiliation by February 2017. NAGPRA states that if a “preponderance of evidence” standard for showing cultural affiliation is not met, a set of rules called “unclaimed regulations,” which the U.S. Department of the Interior added in November 2015, can be applied to the remains. These regulations would allow the Corps to turn over the skeleton to a claimant who could meet the lower standard of showing “substantial evidence” of cultural affiliation. “His reburial is inevitable at this point,” says James Chatters, a local forensic anthropologist who was called in to remove the skeleton from the riverbank when it was discovered in 1996. Chatters adds that the unclaimed regulations could effectively end the study of human remains in the U.S. that predate European contact.

Chatters believes the available genetic information only shows Kennewick Man shares ancestry with all Native Americans, and that it is an overinterpretation of the evidence to say that he is more closely related to native people in the northwestern U.S. than those in other parts of North America. He would like to see additional noninvasive testing done on the remains—stable isotope analysis to determine where the individual came from and micro computed tomography scanning to create a detailed record of the bones—before they are reburied. “Keep the record,” he says, “but let the remains go back in the ground.”

For Chuck Sams, the communications director of the Confederated Tribes of the Umatilla Indian Reservation, the genetic evidence showing the Ancient One was ancestral to Native Americans is a vindication of what he and other members of his community have argued all along. “We are the first people on this landscape,” Sams says, adding that he hopes there will be cultural and legal recognition that archaeological remains found in the Columbia Plateau will be treated as the cultural heritage of the tribes who live there now. “The people of the Confederated Tribes of the Umatilla Indian Reservation along with the other tribes have waited for this day to come, have prayed for this day to come and are looking forward to the day when it finally does arrive for us to be able to lay our ancestor to rest again.”