At the northern edge of The Pit, Port Authority officers, city cops and firefighters were raking through the last of the debris, still finding fragments of bone. At the opposite corner, ironworkers were preparing to cut the last erect piece of steel, a 36-foot-tall girder that had stood at the core of the south tower."Column 1001 B," said Lt. John Ryan, commander of the PA police recovery task force.Ryan pointed out the evenly spaced rectangles where the exterior columns had been. The rectangles marked off an acre in ghostly gray dirt where the tower once stood.There's one," Ryan said.He pointed...