APY,
What Dan lkaf zchus is there to a prosecutor? That he wasn’t intenyltionally malicious, perhaps. Doesn’t mean you have to believe that the allegations against the defendant is true.
You think the Halacha of Dan lkaf zchus is only where a non Jew or a mumar is making the claim? Nonsense.
The only way a non Jew or a mumar enters into the equation is that there is no din of being Dan lkaf zchus on them.