IOWA CITY, Iowa (AP) – The National Park Service is “astonished” that superintendents at a Native American burial ground were able to damage its resources for decades, but the cases point to wider problems inside the agency, according to a report released Thursday.

The agency released a 50-page review examining what went wrong in two high-profile debacles at Effigy Mounds National Monument in northeast Iowa and how to prevent similar damage in the future. The report identified agency shortcomings that include a failure to allow whistleblowing, a lack of training on cultural resources, and a system in which decisions are made by few employees and others feel powerless to question them.

In the first case, Superintendent Thomas Munson in 1990 stole the museum’s collection of ancient human remains and hid them in his garage for two decades to avoid a federal law requiring them to be returned to affiliated tribes. He was recently sentenced to one year in home confinement after investigators eventually recovered the bones.

In the second case, Superintendent Phyllis Ewing oversaw a $3.4 million building spree that constructed a system of boardwalks through the monument’s 200 burial and ceremonial mounds. The 78 projects from 1999 to 2010 showed “little or no compliance” with two federal laws, the National Historic Preservation Act and the Archaeological Resources Protection Act, the review said. Both scandals outraged the tribes that trace their ancestors to the site. They took issue with the bones going missing and the burial sites being built over without any consultation.

“Looking back, everyone is astonished that the incidents at Effigy Mounds National Monument could have happened over so many years,” the report says. The two-year review found “breaks in the system of checks and balances and the line of authority, which allowed those who were culpable to prevail for so long.”

The report said agency employees who were aware that cultural resources were being harmed didn’t act because of complacency, not wanting to hurt feelings and a fear of retaliation. Those who did try to speak up were ignored or punished by their superiors and had no other “clear path for whistleblowing,” the report said.

Superintendents made decisions with an inner circle and kept other employees uninformed, a decision-making process that is widespread in the agency, the report said. They faced little oversight from the Midwest Regional Office in Omaha, where the deputy director had the “impossible responsibility” of trying to supervise 60 superintendents, the report said.

“Overall, there is a general feeling of disenfranchisement among staff at all levels of the National Park Service,” the report says.

It also concluded that the agency has no formal process for employees to report the mismanagement of cultural resources they are supposed to protect. The report includes dozens of recommendations meant to increase training on cultural resources, educate employees about federal laws and the penalties for breaking them, and empowering workers to speak out.