Agency spokeswoman Patty Rooney said that the "principal staff persons involved are no longer employed."
Former park employee Timothy Mason filed a 2010 complaint that sparked the criminal investigation by park service special agent David Barland-Liles after whistleblowers gave him information. The U.S. Attorney's Office declined to press civil or criminal charges against anyone in 2012.
A lifelong park user, Mason called on the agency to "remove all of that illegal, obtrusive junk." Rooney said the boardwalks' future would be decided soon.
The documents included a 2010 memo sent by Regional Director Ernest Quintana to the National Park Service Director Jon Jarvis warning that the illegal construction "had major, adverse impacts to cultural landscapes and to aboriginal American Indian structures that (the site) was established to protect."
Quintana later told Barland-Liles that he kept Ewing as superintendent after the 2009 audit uncovered widespread violations, saying he wanted to give her the chance to help the park recover and prove herself as a manager.
Quintana, now retired, said he didn't consider firing Ewing because she had "no devious design to do something wrong." In 2010, she agreed to transfer to a non-supervisory position in Omaha rather than resign, he said.
Carroll said Ewing's recent firing was based on allegations that she failed to perform duties and follow guidelines dating to her tenure as superintendent, which began in 1999. She's pursuing an internal complaint alleging gender and age discrimination.
Ewing believed that subordinates were carrying the projects out legally and has taken responsibility for inadvertent errors, defense attorney Guy Cook said.
Sinclair, the former maintenance chief who recently left the agency, has no comment, his wife said. He urged prosecutors to "have mercy" in a 2012 interview with Barland-Liles, saying Ewing put him in charge of compliance even though he wasn't familiar with the law.