Postal workers are back on the job at a sorting facility in Tennessee, hours after a co-worker turned it into a crime scene. Colleagues say a letter carrier fatally shot a supervisor and manager before dying from a self-inflicted gunshot. Authorities have not described a motive or officially identified the dead. But a colleague says all postal workers nationwide are under stress. They say the pandemic has added long hours and pressure to their jobs as COVID infections cause absences and new hires don’t know the routines.