If you read the Ramos/Compean transcripts, you will see that prosecutor Kanof told the jury in her summation that if Ramos&Compean had reported the shooting they would have been cleared, and that, indeed, BP agents are always cleared when they report a shooting. Hernandez reported this shooting, and the sheriff and Texas Rangers were not going to prosecute.
Kanof didn't want to tell the real story: if Mexico tells Sutton to prosecute, he will do his damndest to do so, and will seek the harshest possible punishment, regardless of whether the LEO reports it.
Also note that Sutton wasn't one of the 8 federal prosecutors that Alberto Gonzalez fired recently.