What began as an investigation into the July 2016 derailment of a Washington, D.C., Metro train has uncovered several years’ worth of falsified track inspection records, resulting in dismissals or disciplinary action for more than half of the system’s track inspection staff.

Metro General Manager and CEO Paul J. Wiedefeld on Jan. 26 told the Washington Metropolitan Area Transit Authority’s Safety Committee that sixteen track inspectors and five supervisors have been fired as a result of a recently completed review of inspection records from the past three years. Fourteen others were suspended.

Ten new inspectors have been hired from outside Metro to fill the vacancies, Wiedefeld said.

Suspicions about the reliability of Metro track inspection data arose soon after the July 29 Silver Line derailment in an area undergoing major reconstruction as part of the agency’s SafeTrack accelerated maintenance program. The National Transportation Safety Board determined that lateral movement in the rails—the result of loose and missing interlocking components—caused the train to slip off the track.

Wiedefeld in December told the Safety Committee that comments made by Metro employees regarding inspection activities led the agency to expand its initial investigation. While no arrests were made at the investigation’s conclusion, Wiedefeld reported that prosecutors have been briefed on the findings.

The investigation and dismissals are the latest in Wiedefeld’s efforts to transform Metro’s safety culture since November 2015, when he took the reins. Following the derailment, Mott Macdonald was hired to conduct a comprehensive assessment of the entire 216-mile network, with results due in late spring. The company also is revising Metro’s track inspection manual. Metro has retained University of Tennessee faculty to conduct refresher training courses for Metro track inspectors.