McALLEN, Texas—Federal prosecutors have charged a former Department of Homeland Security special agent for his alleged role in a conspiracy to falsify investigative documents before an internal agency review.

Documents filed Monday in federal court in Brownsville say former special agent Wayne Ball signed and backdated falsified reports, indicating investigative activity had taken place where none actually had. Ball is the first to be charged in an investigation that started after an internal review in late 2011.

The investigation's focus has been the Homeland Security Inspector General's Office in McAllen where Ball worked. Court documents indicate a supervisor and another special agent were also involved, but they are not identified.

Ball's attorney declined to comment Monday when reached by The Associated Press.