The U.S. Department of Justice logo is before a news conference, Monday, May 4, 2026, in Washington. Julia Demaree Nikhinson/APThe Department of Justice announced Wednesday that it had opened an investigation into a northern Virginia prosecutor over what it alleged were “sweetheart deals” he cut for immigrants accused of serious crimes.The probe’s target is Fairfax County Commonwealth's Attorney Steve Descano, who denied any wrongdoing in a post…