As others have posted, the charge is not that the convicted agents filed a false report, but that they didn't file any written report. However, BP rules did not require them to do so, anyway. The supervisors who were supposed to file reports did not do so, yet those supervisors were given immunity by the prosecutors, who were determined to make Ramos and Compean the scapegoats.
And let's quit this nonsense of saying juries never make mistakes. If juries are always perfect, why do we have people who were on death row for years suddenly discovered to have been completely innocent all along, thanks to DNA evidence? Everyone-- prosecution, judge, jury--was damn sure they were guilt, and everyone was wrong.