scene, everybody single piece of evidence is critical because, for one, you have to decide how the device functioned. and in finding out how the device functioned, you look if there's a circuitry involved. where in most of his devices, he created the circuitry. and it was not through a timer like many bombers use. he actually took the time to create the mechanism to create the circuits. and that made it really difficult for investigators. >> he built his own switches for the bombs from hickory. and when he bought batteries, he would peel off the covers of the batteries so we wouldn't be able to go back and trace where those batteries might have been purchased. >> there was no evidence that would lend itself to take us to a particular manufacturer, vendor, sales documents, a person's name on a purchase order. there wasn't anything like that connected with the devices. >> but as the attacks continued,