IIRC, WI AG Keith Ellison drove prosecuting the case. My WAG is that DA Gravely knew it was a sure loss, pawned it off on assistants, so the loss wouldn't affect his political ambitions, and chose the least ethical in his office as an act of contempt for the whole steaming pile of a case.
IOW, Gravely has zero credibility, zero honor, zero ethics. If your WAG is true (they levied charges against KR 48 hours after the incident, so their "investigation" was about as thorough as a 4-year-old's crayon drawing), it illustrates how utterly contemptible Gravely is. We don't know the conversation that took place between the two, but if Gravely can't tell the WI AG to pound sand up his ass, he's useless.
Ellison is a Muslim communist, so it stands to reason he'd trade places with Pontius Pilate if he could just to get the opportunity to sentence Jesus to crucifixion.