The remains of Native American ancestors showed up in boxes on the doorsteps of Colorado museums and at yard sales in Denver neighborhoods.

They sat for decades in metal sheds in the state’s national parks and in the bowels of prominent universities.

These human remains were excavated — looted — from the earth that protected them for centuries, in some cases so scientists could study their skulls to prove bogus, racist theories about the Indigenous peoples that lived here for millennia before Europeans displaced them from their ancestral homeland.

Thirty-three years ago, the U.S. Congress attempted to right some of the wrongs of the country’s genocide of American Indians by passing a law designed to give back to tribes these remains, these ancestors, who filled galleries at America’s top universities and museums.

But three decades after the passage of the Native American Grave Protection and Repatriation Act, more than half of those human remains have still not been handed back to tribes and descendants. A ProPublica investigation titled “The Repatriation Project” published last month found 10 institutions hold about half of the 110,000 Native American remains that have languished in collections from Massachusetts to California.

Colorado has been viewed as a national leader in complying with NAGPRA, as the 1990 law is known, with the Denver Museum of Nature & Science and the University of Colorado’s Museum of Natural History two of the first institutions in the country to repatriate their entire collections. Institutions in the state, including federal agencies with offices here, have made available 95.6% of the more than 5,000 Native American remains they had possessed — double the national rate.

But despite those successes, at least 230 Native American ancestors still sit in a handful of Colorado museums and university collections, a ProPublica database shows. All are deemed “culturally unidentifiable” — a designation that experts say has been commonly used to absolve institutions from taking action.

Meanwhile, more than 500 ancestral remains taken from Colorado still sit in collections across the country.

“It’s imperative that institutions that have that 0% (returned) ask themselves the critical questions: How do we see these ancestral remains or items in our possession?” said Theresa Pasqual, director of the Acoma Pueblo’s tribal historic preservation office in New Mexico. “Do we have an ethical and moral right to continue to hold onto these remains or are we ethically obligated to go beyond just sending out a simple letter… and do our due diligence to track down living descendent communities?”

Eugenics and grave robbers ProPublica’s project sent shockwaves through the museum and university world, prompting an avalanche of renewed attention on the progress of institutions across the country in conforming with the landmark 1990 law.

But for those working for years to comply with the act, it confirmed what they already knew: Some of America’s most prestigious institutions — like Harvard University, the University of California, Berkeley and the Field Museum in Chicago — are woefully behind on the 33-year-old legislation.

“It’s sort of a public secret that there are some institutions that have chosen to return only very small portions of their collections,” said Chip Colwell, a former curator at the Denver Museum of Nature & Science.

The law stemmed from a 1987 hearing held by the U.S. Select Committee on Indian Affairs. Smithsonian Secretary Robert McCormick Adams, in testimony on a bill that would repatriate Indian artifacts, indicated more than 50% of the institution’s 34,000 human remains were North American Indians or Alaska Natives.

“Tribal reaction to Secretary Adams’ testimony was swift,” a 1990 Senate report stated. In the following months, Native American tribes around the country called for the repatriation of their ancestors so they could be properly reburied.

American institutions, over the 19th and 20th centuries, accumulated hordes of Native American remains. The Smithsonian in the 1870s paid U.S. soldiers hefty sums for Indian clothing, weapons and tools to be sent back to Washington, ProPublica reported.

“We had these collections from well-known grave robbers that went throughout our country and dug everything up,” said Richard Smith, the historic preservation officer for the Pueblo of Laguna tribe in New Mexico.

Part of the fascination of early archeologists centered around the eugenics movement, which gained significant popularity in the United States from the late 19th century into the early 20th century.

Eugenics — the racist idea of improving the quality of the human race by encouraging the reproduction of people with desirable traits — counted as prominent supporters Theodore Roosevelt, Alexander Graham Bell and John D. Rockefeller Jr., among others.

It also led institutions like the University of Denver to acquire Native American skulls to be studied. Eugenics was “definitely what our founder (Dr. Etienne B. Renaud) was interested in,” said Anne Amati, DU’s NAGPRA coordinator.

Renaud, like other scientists, collected looted craniums in an effort to prove a racist theory that Indigenous people were inferior to white people based on their skull sizes.

Federal records maintained by National Park Service, which oversees NAGPRA, show how DU and other Colorado institutions accumulated thousands of Native American remains from across the southwest.

DU’s Department of Anthropology used the remains of 17 individuals that had been removed from unknown locations as teaching aids in a professor’s “dig lab” in the 1980s, recreating an archaeology site in the Science Hall basement, the school wrote in a 2016 notice.

“Museums accepted these people because they thought for a long time that natural history museums have a duty to curate and study everything in the natural world — including and especially Native Americans,” Colwell said.

But museums often didn’t keep — or never received — detailed records for the remains in their collections.

“It’s always fascinating to me how many people out there have Native American human remains in their grandfather’s attic or something,” said Glenys Ong Echavarri, History Colorado’s former NAGPRA liaison and tribal consultation coordinator.

“A barrier to repatriation” After the law’s passage in 1990, Congress envisioned that nearly all repatriations would be completed within five years.

It’s now been 33 years — and Colwell estimates we’re at least 70 years away from completion at the current pace. The Biden administration is now seeking regulatory changes to NAGPRA that would expedite repatriation proceedings and streamline the process for institutions.

Experts point to a lack of enforcement by the federal NAGPRA program, no firm deadlines on repatriations and a lack of resources among tribes and museums.

But many institutions have used a particular designation — “culturally unidentifiable” — to thwart attempts by tribes to reclaim their ancestors. These include remains in which “no lineal descendant or culturally affiliated Indian tribe or Native Hawaiian organization has been determined,” according to the law.

Some major repositories, including the Ohio History Connection and the University of Tennessee, Knoxville, categorized everything in their collection that might be subject to the law as “culturally unidentifiable,” ProPublica found.

“It is clear that has been a barrier to repatriation,” Melanie O’Brien, program manager for the National NAGPRA Program, told The Denver Post.

Since NAGPRA became law, 28 institutions located in Colorado reported Native American remains in their collections that were taken from across the country, according to ProPublica’s data. Of the 5,285 total remains that at one time were housed here, 5,055 have been made available for return to tribes — or 95.6%.