Most of the files of the recent cases had to do with the Leaky Cauldron explosion. There was a large number of suspected perpetrators that they were trying to weed through. Even being out of the game for as long as she had been, Hermione could tell just by reading their files that at least ninety percent of them were innocent. Likely only brought to the Ministry because they were suspected of holding less than glowing opinions about the regime. It was how these things worked.