The National Transportation Safety Board's investigation into the cause of the 35W bridge collapse has revealed damage in part of the bridge structure that the agency says warrants further inspection. Investigators say they have "observed damage in some gusset plates," the metal plates that held the bridge's steel beams together. A week after the bridge collapsed, the NTSB said the agency had identified what it called a design issue with gusset plates at certain locations on the bridge. Officials say they have not yet recovered all of the gusset plates from the Mississippi, so it is still impossible to say whether the gusset plates played a significant role in the collapse. But NTSB spokesman Terry Williams says the agency is not ruling anything out.