CHICAGO — Back in March, a high-ranking Cook County prosecutor sent an email that by her own admission was “desperate.” A jury trial was scheduled to start soon in traffic court. But there weren’t enough staffers to handle both the trial and the regular traffic cases at the same time. So the deputy chief of the Criminal Prosecutions Bureau sent out a call for volunteers: Could any prosecutors come help with the grunt work for a week? “I would not be asking this if it wasn’t such a desperate situation,” she wrote. A few months later, on a Monday morning in July, a murder trial was scheduled to …