Keppler is a dirty cop

I think you missed the whole point of this episode. Keppler wasn't dirty. He spent his entire CSI career trying to attone for the murder of the man who raped his lover/fiance/wife. He was a meticulous criminalist. The final irony is that the man he killed wasn't even the rapist. It is this realization that sets things in motion in the last half of tonight's episode. He must make the last act of attonement by bringing his would-be father-in-law to justice.