st. LOUIS — St. Louis Circuit Attorney Kimberly M. Gardner responded Friday to a judge’s threat to hold her in contempt of court by blaming an attorney for not telling her office he had a trial slated to begin while he was on leave.The filing says prosecutor Alex Polta, who has been on approved leave since early April, failed to warn Gardner’s office about a murder trial that was set to begin last Monday.No one attended the first day of trial in Polta’s place, and Judge Scott A. Millikan filed an order for Gardner’s office to show cause…